Moves backpacks into their own DMI and "standardize" some names (#70220)

I wanted to touch a backpack sprite and got mad with everything being on the same dmi file sooo...
Creates a dmi for backpacks because we had everything shoved on the same back.dmi or storage.dmi which is a headache to work with.

I tried to standardize the name between backpacks, satchels and duffels and some minor clarity while I was there, stuff like:
securitypack -> backpack-security
satchel-sec -> satchel-security
brokenpack -> bag_of_holding-inert

Also made a new obj icon file for the ethereal backpack, it had it's own file for the mob worn icon so now both icons have their own dmi.
Probably should rename it to "species" if we ever add more species/lore related backpacks but that is a future issue.

I didn't touch the inhand dmis or "standardize" their name, they are well split enough and just to avoid making a zillion changes on the same PR.
I might look into it if this PR is merged.

code/game/objects/items/storage/backpack.dm

@@ -12,6 +12,8 @@
 /obj/item/storage/backpack
 	name = "backpack"
 	desc = "You wear this on your back and put items into it."
+	icon = 'icons/obj/storage/backpack.dmi'
+	worn_icon = 'icons/mob/clothing/back/backpack.dmi'
 	icon_state = "backpack"
 	inhand_icon_state = "backpack"
 	lefthand_file = 'icons/mob/inhands/equipment/backpack_lefthand.dmi'
@@ -36,8 +38,9 @@
 /obj/item/bag_of_holding_inert
 	name = "inert bag of holding"
 	desc = "What is currently a just an unwieldly block of metal with a slot ready to accept a bluespace anomaly core."
-	icon = 'icons/obj/storage/storage.dmi'
+	icon = 'icons/obj/storage/backpack.dmi'
-	icon_state = "brokenpack"
+	worn_icon = 'icons/mob/clothing/back/backpack.dmi'
+	icon_state = "bag_of_holding-inert"
 	inhand_icon_state = "brokenpack"
 	lefthand_file = 'icons/mob/inhands/equipment/backpack_lefthand.dmi'
 	righthand_file = 'icons/mob/inhands/equipment/backpack_righthand.dmi'
@@ -48,7 +51,7 @@
 /obj/item/storage/backpack/holding
 	name = "bag of holding"
 	desc = "A backpack that opens into a localized pocket of bluespace."
-	icon_state = "holdingpack"
+	icon_state = "bag_of_holding"
 	inhand_icon_state = "holdingpack"
 	resistance_flags = FIRE_PROOF
 	item_flags = NO_MAT_REDEMPTION
@@ -104,80 +107,80 @@
 /obj/item/storage/backpack/cultpack
 	name = "trophy rack"
 	desc = "It's useful for both carrying extra gear and proudly declaring your insanity."
-	icon_state = "cultpack"
+	icon_state = "backpack-cult"
 	inhand_icon_state = "backpack"
 
 /obj/item/storage/backpack/clown
 	name = "Giggles von Honkerton"
 	desc = "It's a backpack made by Honk! Co."
-	icon_state = "clownpack"
+	icon_state = "backpack-clown"
 	inhand_icon_state = "clownpack"
 
 /obj/item/storage/backpack/explorer
 	name = "explorer bag"
 	desc = "A robust backpack for stashing your loot."
-	icon_state = "explorerpack"
+	icon_state = "backpack-explorer"
 	inhand_icon_state = "explorerpack"
 
 /obj/item/storage/backpack/mime
 	name = "Parcel Parceaux"
 	desc = "A silent backpack made for those silent workers. Silence Co."
-	icon_state = "mimepack"
+	icon_state = "backpack-mime"
 	inhand_icon_state = "mimepack"
 
 /obj/item/storage/backpack/medic
 	name = "medical backpack"
 	desc = "It's a backpack especially designed for use in a sterile environment."
-	icon_state = "medicalpack"
+	icon_state = "backpack-medical"
 	inhand_icon_state = "medicalpack"
 
 /obj/item/storage/backpack/security
 	name = "security backpack"
 	desc = "It's a very robust backpack."
-	icon_state = "securitypack"
+	icon_state = "backpack-security"
 	inhand_icon_state = "securitypack"
 
 /obj/item/storage/backpack/captain
 	name = "captain's backpack"
 	desc = "It's a special backpack made exclusively for Nanotrasen officers."
-	icon_state = "captainpack"
+	icon_state = "backpack-captain"
 	inhand_icon_state = "captainpack"
 
 /obj/item/storage/backpack/industrial
 	name = "industrial backpack"
 	desc = "It's a tough backpack for the daily grind of station life."
-	icon_state = "engiepack"
+	icon_state = "backpack-engineering"
 	inhand_icon_state = "engiepack"
 	resistance_flags = FIRE_PROOF
 
 /obj/item/storage/backpack/botany
 	name = "botany backpack"
 	desc = "It's a backpack made of all-natural fibers."
-	icon_state = "botpack"
+	icon_state = "backpack-hydroponics"
 	inhand_icon_state = "botpack"
 
 /obj/item/storage/backpack/chemistry
 	name = "chemistry backpack"
 	desc = "A backpack specially designed to repel stains and hazardous liquids."
-	icon_state = "chempack"
+	icon_state = "backpack-chemistry"
 	inhand_icon_state = "chempack"
 
 /obj/item/storage/backpack/genetics
 	name = "genetics backpack"
 	desc = "A bag designed to be super tough, just in case someone hulks out on you."
-	icon_state = "genepack"
+	icon_state = "backpack-genetics"
 	inhand_icon_state = "genepack"
 
 /obj/item/storage/backpack/science
 	name = "science backpack"
 	desc = "A specially designed backpack. It's fire resistant and smells vaguely of plasma."
-	icon_state = "scipack"
+	icon_state = "backpack-science"
 	inhand_icon_state = "scipack"
 
 /obj/item/storage/backpack/virology
 	name = "virology backpack"
 	desc = "A backpack made of hypo-allergenic fibers. It's designed to help prevent the spread of disease. Smells like monkey."
-	icon_state = "viropack"
+	icon_state = "backpack-virology"
 	inhand_icon_state = "viropack"
 
 /obj/item/storage/backpack/ert
@@ -215,6 +218,7 @@
 /obj/item/storage/backpack/saddlepack
 	name = "saddlepack"
 	desc = "A backpack designed to be saddled on a mount or carried on your back, and switch between the two on the fly. It's quite spacious, at the cost of making you feel like a literal pack mule."
+	icon = 'icons/obj/storage/ethereal.dmi'
 	worn_icon = 'icons/mob/clothing/back/ethereal.dmi'
 	icon_state = "saddlepack"
 
@@ -235,7 +239,7 @@
 /obj/item/storage/backpack/satchel/leather
 	name = "leather satchel"
 	desc = "It's a very fancy satchel made with fine leather."
-	icon_state = "satchel"
+	icon_state = "satchel-leather"
 	inhand_icon_state = "satchel"
 
 /obj/item/storage/backpack/satchel/leather/withwallet/PopulateContents()
@@ -247,50 +251,50 @@
 /obj/item/storage/backpack/satchel/eng
 	name = "industrial satchel"
 	desc = "A tough satchel with extra pockets."
-	icon_state = "satchel-eng"
+	icon_state = "satchel-engineering"
 	inhand_icon_state = "satchel-eng"
 	resistance_flags = FIRE_PROOF
 
 /obj/item/storage/backpack/satchel/med
 	name = "medical satchel"
 	desc = "A sterile satchel used in medical departments."
-	icon_state = "satchel-med"
+	icon_state = "satchel-medical"
 	inhand_icon_state = "satchel-med"
 
 /obj/item/storage/backpack/satchel/vir
 	name = "virologist satchel"
 	desc = "A sterile satchel with virologist colours."
-	icon_state = "satchel-vir"
+	icon_state = "satchel-virology"
 	inhand_icon_state = "satchel-vir"
 
 /obj/item/storage/backpack/satchel/chem
 	name = "chemist satchel"
 	desc = "A sterile satchel with chemist colours."
-	icon_state = "satchel-chem"
+	icon_state = "satchel-chemistry"
 	inhand_icon_state = "satchel-chem"
 
 /obj/item/storage/backpack/satchel/gen
 	name = "geneticist satchel"
 	desc = "A sterile satchel with geneticist colours."
-	icon_state = "satchel-gen"
+	icon_state = "satchel-genetics"
 	inhand_icon_state = "satchel-gen"
 
 /obj/item/storage/backpack/satchel/science
 	name = "scientist satchel"
 	desc = "Useful for holding research materials."
-	icon_state = "satchel-sci"
+	icon_state = "satchel-science"
 	inhand_icon_state = "satchel-sci"
 
 /obj/item/storage/backpack/satchel/hyd
 	name = "botanist satchel"
 	desc = "A satchel made of all natural fibers."
-	icon_state = "satchel-hyd"
+	icon_state = "satchel-hydroponics"
 	inhand_icon_state = "satchel-hyd"
 
 /obj/item/storage/backpack/satchel/sec
 	name = "security satchel"
 	desc = "A robust satchel for security related needs."
-	icon_state = "satchel-sec"
+	icon_state = "satchel-security"
 	inhand_icon_state = "satchel-sec"
 
 /obj/item/storage/backpack/satchel/explorer
@@ -302,7 +306,7 @@
 /obj/item/storage/backpack/satchel/cap
 	name = "captain's satchel"
 	desc = "An exclusive satchel for Nanotrasen officers."
-	icon_state = "satchel-cap"
+	icon_state = "satchel-captain"
 	inhand_icon_state = "satchel-cap"
 
 /obj/item/storage/backpack/satchel/flat
@@ -370,7 +374,7 @@
 /obj/item/storage/backpack/duffelbag/med
 	name = "medical duffel bag"
 	desc = "A large duffel bag for holding extra medical supplies."
-	icon_state = "duffel-med"
+	icon_state = "duffel-medical"
 	inhand_icon_state = "duffel-med"
 
 /obj/item/storage/backpack/duffelbag/med/surgery
@@ -404,7 +408,7 @@
 /obj/item/storage/backpack/duffelbag/science
 	name = "scientist's duffel bag"
 	desc = "A large duffel bag for holding extra scientific components."
-	icon_state = "duffel-sci"
+	icon_state = "duffel-science"
 	inhand_icon_state = "duffel-sci"
 
 /obj/item/storage/backpack/duffelbag/virology
@@ -431,7 +435,7 @@
 /obj/item/storage/backpack/duffelbag/sec
 	name = "security duffel bag"
 	desc = "A large duffel bag for holding extra security supplies and ammunition."
-	icon_state = "duffel-sec"
+	icon_state = "duffel-security"
 	inhand_icon_state = "duffel-sec"
 
 /obj/item/storage/backpack/duffelbag/sec/surgery
@@ -453,7 +457,7 @@
 /obj/item/storage/backpack/duffelbag/engineering
 	name = "industrial duffel bag"
 	desc = "A large duffel bag for holding extra tools and supplies."
-	icon_state = "duffel-eng"
+	icon_state = "duffel-engineering"
 	inhand_icon_state = "duffel-eng"
 	resistance_flags = FIRE_PROOF