makes door code more OOP: reduced copypasta in shutter and poddoor code, they have their own icon files, changed name of icon_states in the maps

added a few defines and helpers
do_after family supports callbacks
added airlock security levels to airlocks
obj_integrity for doors, door assemblies, firelock frames
vault door assembly is 8 plasteel up from 6
explosion_block works better
heavy firelocks block explosions, firelock (de)construction uses crowbar instead of welder
xenos can open airlocks
minor change to attacking obj message

code/datums/wires/airlock.dm

@@ -164,9 +164,10 @@ var/const/AIRLOCK_WIRE_LIGHT = 512
 			//one wire for door bolts. Sending a pulse through this drops door bolts if they're not down (whether power's on or not),
 			//raises them if they are down (only if power's on)
 			if(!A.locked)
-				A.lock()
-			else
-				A.unlock()
+				if(A.lock())
+					A.audible_message("<span class='italics'>You hear a click from the bottom of the door.</span>", null,  1)
+			else if(A.unlock())
+				A.audible_message("<span class='italics'>You hear a click from the bottom of the door.</span>", null,  1)
 
 		if(AIRLOCK_WIRE_BACKUP_POWER1)
 			//two wires for backup power. Sending a pulse through either one causes a breaker to trip, but this does not disable it unless main power is down too (in which case it is disabled for 1 minute or however long it takes main power to come back, whichever is shorter).