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/OpenRA/OpenRA/pull/6552/files#diff-da0b70bbc22b6b4af2fbe96dd5c5a8b7R19) set to true can help testing.
Lets fix that by adding a `set` property to Owner that calls `Actor.ChangeOwner` if newOwner != existingOwner.