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/pda/PDA.dm

@@ -169,7 +169,7 @@ var/global/list/obj/item/device/pda/PDAs = list()
 	data["useRetro"] = retro_mode
 
 	data["cartridge_name"] = cartridge ? cartridge.name : ""
-	data["stationTime"] = worldtime2text()
+	data["stationTime"] = station_time_timestamp()
 
 	data["app"] = list()
 	current_app.update_ui(user, data)