Lighting overhaul.

This commit overhauls the lighting system to Bay12 standards. It is better
in pretty much every way.

code/modules/lighting/lighting_process.dm

@@ -0,0 +1,23 @@
+/datum/controller/process/lighting/setup()
+	name = "lighting"
+	schedule_interval = LIGHTING_INTERVAL
+
+	create_lighting_overlays()
+
+/datum/controller/process/lighting/doWork()
+	for(var/datum/light_source/L in lighting_update_lights)
+		if(L.needs_update)
+			if(L.destroyed)
+				L.remove_lum()
+			else if(L.check() || L.force_update)
+				L.remove_lum()
+				L.apply_lum()
+				L.force_update = 0
+			L.needs_update = 0
+	lighting_update_lights.Cut()
+
+	for(var/atom/movable/lighting_overlay/O in lighting_update_overlays)
+		if(O.needs_update)
+			O.update_overlay()
+			O.needs_update = 0
+	lighting_update_overlays.Cut()