Shuttle refactor (#2171)

Rewrites the area movement code used by shuttles & elevators in an effort to make it faster, more extensible, and generally easier to read. Also fixes some bugs relating to lighting & moving areas, such as lighting overlays suddenly being teleported into space for absolutely no reason.

Fixes #2161.
Fixes #2166.

code/controllers/subsystems/explosives.dm

@@ -32,7 +32,7 @@ var/datum/controller/subsystem/explosives/SSexplosives
 	if (!(work_queue.len))
 		ticks_without_work++
 		if (powernet_update_pending && ticks_without_work > 5)
-			makepowernets()
+			SSmachinery.powernet_update_queued = TRUE
 			powernet_update_pending = 0
 
 			// All explosions handled, powernet rebuilt.

code/controllers/subsystems/machinery.dm

@@ -23,6 +23,7 @@
 	var/list/breaker_boxes = list()
 
 	var/rcon_update_queued = FALSE
+	var/powernet_update_queued = FALSE
 
 	var/list/slept_in_process = list()
 
@@ -69,6 +70,10 @@
 		if (rcon_update_queued)
 			build_rcon_lists()
 
+		if (powernet_update_queued)
+			makepowernets()
+			powernet_update_queued = FALSE
+
 	var/list/curr_machinery = src.processing_machinery
 	var/list/curr_powersinks = src.processing_powersinks