Materials subsystem, material defines instead of strings, structure materials. (#8447)

The shitcode crusade begins.

code/game/objects/structures.dm

@@ -8,6 +8,7 @@
 	var/parts
 	var/list/climbers
 	var/list/footstep_sound	//footstep sounds when stepped on
+	var/material/material
 
 /obj/structure/Destroy()
 	if(parts)
@@ -187,5 +188,9 @@
 		return 0
 	visible_message("<span class='danger'>[user] [attack_verb] the [src] apart!</span>")
 	user.do_attack_animation(src)
-	spawn(1) qdel(src)
+	spawn(1)
+		qdel(src)
 	return 1
+
+/obj/structure/get_material()
+	return material