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.
This is subject to further balancing. It should be done per-map. A simple test shows that Death Depts is too small and too open to have even 3 worms early on. Other maps will handle them fine. On most maps 8 worms would be ridiculous. On a few it could be OK.
I will set those to 2 and 4 respectively for the sake of this being easier to test without changing the maps.