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/e14ca26efa88f43f7da30762e2bc96975a6fc2d3#diff-da0b70bbc22b6b4af2fbe96dd5c5a8b7R15)).

[This](https://github.com/abcdefg30/OpenRA/commit/e14ca26efa88f43f7da30762e2bc96975a6fc2d3#diff-da0b70bbc22b6b4af2fbe96dd5c5a8b7R18) set to true can help testing.
This works surprisingly well, but probably wants to use cell triggers instead. https://github.com/OpenRA/OpenRA/pull/6574