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.
The cleanest way may be to create a new `WithAttackOverlay` trait. Get some inspiration from the existing With*Overlay render traits. Don't really have a good suggestion which interface to use though. It may be easier to just hard-code the trait look-up and play the new animation here.