Change all AI packages (except AiActivate) to use ActorIds

More robust in case the target changes cell or there are multiple targets with the same RefId
AiCombat: Removed obsolete door back-off code (now handled in AiAvoidDoor)
Fix a potential exploit that made it possible to reset the owner of any item
Fix item owner not resetting when dragging an item from a corpse to the player avatar
Fix player not being allowed to use his own items