Portable Ladders (#2434)

Add portable ladders as items.
Deploy on floors that have an open space above them, and in open spaces that have floors beneath them.
Fold them, to reuse them.

Need item,structure base and structure body sprites. Probably an in hand sprite too.

code/modules/multiz/structures.dm

@@ -123,6 +123,27 @@
 	allowed_directions = UP|DOWN
 	icon_state = "ladder11"
 
+/obj/structure/ladder/mobile/base
+	allowed_directions = UP
+	icon_state = "ladder11"
+/obj/structure/ladder/mobile/body
+	allowed_directions = DOWN
+	icon_state = "ladder11"
+
+/obj/structure/ladder/mobile/verb/fold()
+	set name = "Fold Ladder"
+	set category = "Object"
+	set src in oview(1)
+	var/obj/item/weapon/ladder_mobile/R = new(src.loc)
+	src.transfer_fingerprints_to(R)
+	
+	if(src.target_down == null)
+		QDEL_NULL(src.target_up)
+		qdel(src)
+	else
+		QDEL_NULL(src.target_down)
+		qdel(src)
+
 /obj/structure/stairs
 	name = "Stairs"
 	desc = "Stairs leading to another deck.  Not too useful if the gravity goes out."