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.
These brackets are unnecessary.
[Coding Standard](https://github.com/OpenRA/OpenRA/wiki/Coding-Standard#the-short-version):
> Braces around code blocks should reside on their own line, and should be omitted if the block contains a single statement.