Further process tweaks

- Integrates Volundr's btime library and associated process scheduler
changes.
- btime is implemented separately from the process scheduler, as precise
time measurement is also useful elsewhere.
- `TimeOfHour` is no longer internally throttled; throttling is instead
done by `SCHECK`.
- If btime's `gettime` cannot be called at world startup, an error will
be output and the world will stop.
- Retains the change to schedule processes according to game time,
rather than real time.
- Removes the (now unused) update queue files.
- Removes the process scheduler testing files.
- These are standalone tests for the process scheduler, completely
unrelated to its use in the full codebase. We never used them.
- Moves the process scheduler defines into __DEFINES.
- Makes the lighting process run once before the round starts.
- Renames `scheck` to `sleepCheck`, to ensure any code that tries to use
`scheck` will fail to compile.
- Adds `SCHECK` and `SCHECK_EVERY` macros that skip calling `sleepCheck`
entirely until a specified number of `SCHECK`s (50 by default) have been
called.
- Makes most processes iterate using their `last_object` variable,
allowing hang recovery to show the type that caused the hang.
- Makes processes output an error when they filter out a type they
refuse to process.
- Rolls the recently-added alarm subsystem into the alarm process.
- Removes the now unused subsystems code.

code/controllers/subsystem/alarms.dm

@@ -1,30 +0,0 @@
-// We manually initialize the alarm handlers instead of looping over all existing types
-// to make it possible to write: camera.triggerAlarm() rather than alarm_manager.managers[datum/alarm_handler/camera].triggerAlarm() or a variant thereof.
-/var/global/datum/alarm_handler/atmosphere/atmosphere_alarm	= new()
-/var/global/datum/alarm_handler/camera/camera_alarm			= new()
-/var/global/datum/alarm_handler/fire/fire_alarm				= new()
-/var/global/datum/alarm_handler/motion/motion_alarm			= new()
-/var/global/datum/alarm_handler/power/power_alarm			= new()
-
-/datum/subsystem/alarm
-	name = "Alarm"
-	var/list/datum/alarm/all_handlers
-
-/datum/subsystem/alarm/New()
-	all_handlers = list(atmosphere_alarm, camera_alarm, fire_alarm, motion_alarm, power_alarm)
-
-/datum/subsystem/alarm/fire()
-	for(var/datum/alarm_handler/AH in all_handlers)
-		AH.process()
-
-/datum/subsystem/alarm/proc/active_alarms()
-	var/list/all_alarms = new
-	for(var/datum/alarm_handler/AH in all_handlers)
-		var/list/alarms = AH.alarms
-		all_alarms += alarms
-
-	return all_alarms
-
-/datum/subsystem/alarm/proc/number_of_active_alarms()
-	var/list/alarms = active_alarms()
-	return alarms.len