Nightshifts & Randomized Station Time

This commit adds the Nightshift lighting mode from /tg/. From 19:00 to
07:00 in station time, the station will go into a reduced-lighting mode,
with dimmed lights across the station.

In conjunction with this, there is a new configuration option to start
the shift time at a random time other than 12:00, so that players are
more likely to experience a night shift (as opposed to having to have a
7 hour round).

code/modules/security_levels/security levels.dm

@@ -123,6 +123,7 @@
 			atc.reroute_traffic(yes = TRUE) // Tell them fuck off we're busy.
 		else
 			atc.reroute_traffic(yes = FALSE)
+		SSnightshift.check_nightshift()
 
 	else
 		return