Savegame: store levelled creature state and move to actorIds

(Closes #1332)
Fix a wrong use of reference that causes potential crash
Savegame: store door movement state (Closes #747)
Fix exception when getting hit by a trap
Fix searching the player's actorId
Add some more safety checks to spellcasting
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
Fix searchPtrViaActorId not skipping over deleted references

Fixes an issue when an actor has moved cell: searchPtrViaActorId would randomly return the deleted Ptr from the old cell.