Code rework of placing things on walls.

Stuff goes under types.
Types have procs.
Never have 500 lines of repeated code again.

I came very close to crying while editing this. You should appreciate
that.

----

This commit entirely reworks how placing things on walls work- Posters
have intentionally been left alone to reduce the amount of lines
changed. With this commit, wall-mounted objects are no longer snowflaked
into the wall file.

code/game/objects/items/mountable_frames/frames.dm

@@ -0,0 +1,25 @@
+/obj/item/mounted/frame
+	name = "mountable frame"
+	desc = "Place it on a wall."
+	var/sheets_refunded = 2
+	var/list/mount_reqs = list() //can contain simfloor, nospace. Used in try_build to see if conditions are needed, then met
+
+/obj/item/mounted/frame/attackby(obj/item/weapon/W, mob/user)
+	..()
+	if (istype(W, /obj/item/weapon/wrench) && sheets_refunded)
+		//new /obj/item/stack/sheet/metal( get_turf(src.loc), sheets_refunded )
+		var/obj/item/stack/sheet/metal/M = getFromPool(/obj/item/stack/sheet/metal, get_turf(src))
+		M.amount = sheets_refunded
+		qdel(src)
+
+/obj/item/mounted/frame/try_build(turf/on_wall, mob/user)
+	if(..()) //if we pass the parent tests
+		var/turf/turf_loc = get_turf(user)
+
+		if (src.mount_reqs.Find("simfloor") && !istype(turf_loc, /turf/simulated/floor))
+			user << "<span class='rose'>[src] cannot be placed on this spot.</span>"
+			return
+		if (src.mount_reqs.Find("nospace") && (areaMaster.requires_power == 0 || areaMaster.name == "Space"))
+			user << "<span class='rose'>[src] cannot be placed in this area.</span>"
+			return
+		return 1