Initial implementation of Sandworms (WIP; Need help with audio and animations)

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.
That may want to live in a separate trait then. I think RA2 has voice notifications for "enemy unit sighted" so it can be reused when implemented in a modular way.