Vent Clog and False Alarm events: Attempt 2 (#850)

New PR to fix merge issues

Porting an event from tg. Scrubbers get clogged and eject some chemical smoke with potentially fun effeects

I looked through chemsmoke code while doing this, and found it wanting, so i improved it. Added a duration input, adjusted all uses of chemsmoke in the code. Generally gave them all higher durations, chemsmoke grenades were a disappointing poot

Adds a new mundane event, false alarm.
It picks a random moderate or severe event and fakes its announcement without actually running the event.

Three minutes later, CC sends another announcement apologising for the false alarm

Also added an event var allowing events to exclude themselves from being picked for faking

code/modules/events/false_alarm.dm

@@ -0,0 +1,37 @@
+//False Alarm Event
+//This picks a random moderate or severe event and fakes its announcement
+//without actually running the event
+//After roughly 3 minutes, CC sends another announcement apologising for the false alarm
+
+/datum/event/false_alarm
+	announceWhen	= 0
+	endWhen	=	90
+	var/datum/event_meta/EM
+
+
+/datum/event/false_alarm/end()
+	command_announcement.Announce("Error, It appears our previous announcement about a [EM.name] was a sensor glitch. There is no cause for alarm, please return to your stations.", "False Alarm")
+
+
+/datum/event/false_alarm/announce()
+	var/datum/event_container/EC
+	if (prob(50))
+		EC = event_manager.event_containers[EVENT_LEVEL_MODERATE]
+	else
+		EC = event_manager.event_containers[EVENT_LEVEL_MAJOR]
+
+	//Don't pick events that are excluded from faking.
+	EM = pick(EC.available_events)
+	var/datum/event/E = null
+	var/fake_allowed = 0
+	while (!fake_allowed)
+		if (E)
+			E.kill(0)
+		EM = pick(EC.available_events)
+		E = new EM.event_type(EM)
+		fake_allowed = !E.no_fake
+
+	message_admins("False Alarm: [E]")
+	E.kill(0)
+	E.announce()
+