fixes and balance

Fixes:

* Depot mobs now generate attack animations when you attack them.

* Depot mobs can no longer be endlessly spammed with melee item attacks. This counters the 'spam attacks till you get lucky' strategy.

* Depot mobs can no longer be harmed by punching them. This counters the 'bypass eshield with punches' strategy.

* Depot mobs will now kill you if you're in crit. This counters endlessly-regenerating diona.

* Syndicate sentry bot will now path through other depot mobs. This fixes the bot getting stuck on them.

Balance tweaks:

* Armory airlocks are now harder to hack.

* Armory is now protected by an energy shield. Killing officers may randomly unlock the shield. This counters people rushing the armory every time. Depot mobs can walk through the shield.

* Depot mobs (except for the bot) now recogize if you've returned from death to attack them again, and increase the alert level further. This counters changelings.

code/game/objects/structures/depot.dm

@@ -70,6 +70,7 @@
 		if(!depotarea.used_self_destruct)
 			depotarea.used_self_destruct = TRUE // Silences all further alerts from this point onwards.
 			depotarea.updateicon()
+		depotarea.shields_down()
 
 /obj/effect/overload/process()
 	if(cycles < max_cycles)
@@ -91,3 +92,4 @@
 	explosion(get_turf(src), 25, 35, 45, 55, 1, 1, 60, 0, 0)
 	processing_objects.Remove(src)
 	qdel(src)
+