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.
You may want to move this functionality into https://github.com/OpenRA/OpenRA/wiki/Traits#announceonkill However that trait need adjustments so it does not use the (neutral) owner of the killer, but the house voice of the target.