D2k: Sandworms implementation

Using Mailaender's code as basis, this is my implementation of the sandworm behavior. It is still WIP, but you can get an idea of how it looks from the shellmap.
I would prefer we fixed AttackWander directly instead of duplicating this.  A simpler approach would be to walk outwards in the direction of the target while the actor can move instead of trying / failing / reducing.