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/fire_alarm.dm

@@ -0,0 +1,10 @@
+/obj/item/mounted/frame/firealarm
+	name = "fire alarm frame"
+	desc = "Used for building Fire Alarms"
+	icon = 'icons/obj/monitors.dmi'
+	icon_state = "fire_bitem"
+	mount_reqs = list("simfloor", "nospace")
+
+/obj/item/mounted/frame/firealarm/do_build(turf/on_wall, mob/user)
+	new /obj/machinery/firealarm(get_turf(src), get_dir(on_wall, user), 1)
+	qdel(src)