Porting multi-z support updates.

code/modules/mob/dead/observer/observer.dm

@@ -17,6 +17,7 @@ GLOBAL_VAR_INIT(observer_default_invisibility, INVISIBILITY_OBSERVER)
 	see_in_dark = 100
 	invisibility = INVISIBILITY_OBSERVER
 	hud_type = /datum/hud/ghost
+	movement_type = GROUND | FLYING
 	var/can_reenter_corpse
 	var/can_reenter_round = TRUE
 	var/datum/hud/living/carbon/hud = null // hud

code/modules/mob/dead/observer/observer_movement.dm

@@ -0,0 +1,2 @@
+/mob/dead/observer/canZMove(direction, turf/target)
+	return TRUE