Replaces /image with /mutable_appearance (#556)

* Replaces /image with /mutable_appearance, where appropriate

* Update miscellaneous.dm

* Delete miscellaneous.dm.rej

* Delete pet.dm.rej

* Update pet.dm

* Update species.dm

* Update miscellaneous.dm

* Update species.dm

* Update miscellaneous.dm

* Delete species.dm.rej

* Update species.dm

pretty sure I got all the indentation correct THIS time, ffs

* Update species.dm

* Update species.dm

fucking tabs man, fucking tabs.

code/game/objects/structures/guncase.dm

@@ -7,7 +7,7 @@
 	anchored = 0
 	density = 1
 	opacity = 0
-	var/case_type = null
+	var/case_type = ""
 	var/gun_category = /obj/item/weapon/gun
 	var/open = 1
 	var/capacity = 4
@@ -25,8 +25,10 @@
 /obj/structure/guncase/update_icon()
 	cut_overlays()
 	if(case_type && LAZYLEN(contents))
+		var/mutable_appearance/gun_overlay = mutable_appearance(icon, case_type)
 		for(var/i in 1 to contents.len)
-			add_overlay(image(icon = src.icon, icon_state = "[case_type]", pixel_x = 3 * (i - 1) ))
+			gun_overlay.pixel_x = 3 * (i - 1)
+			add_overlay(gun_overlay)
 	if(open)
 		add_overlay("[icon_state]_open")
 	else