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).~~ See below.

[This](https://github.com/abcdefg30/OpenRA/commit/a7b14dfcef2cdb3450f4f6d179c515d13ec52ff4#diff-da0b70bbc22b6b4af2fbe96dd5c5a8b7R19) set to true can help testing.
You should be able to simplify this block down to `var emergingStance = Enum<Stance>.Parse(newStance);`