Ported monster tank madness to lua

It would be nice, if someone could already have a look at this (style nits?),
although this is not completely finished yet (see [todo](https://github.com/abcdefg30/OpenRA/commit/6acfec46409285ed52c9d2b5c6dc7e1398981a1a#diff-da0b70bbc22b6b4af2fbe96dd5c5a8b7R15)).

[This](https://github.com/abcdefg30/OpenRA/commit/6acfec46409285ed52c9d2b5c6dc7e1398981a1a#diff-da0b70bbc22b6b4af2fbe96dd5c5a8b7R18) set to true can help testing.
`playerUnits`