Ported allies-03a-classic

Could someone confirm, that I used the correct videos, please?

Two todos left:
- I wanted some buildings to be sold.
(Like in the original mission.)
- The engineer is glitchy.
Oh no, https://github.com/OpenRA/OpenRA/wiki/Traits#luascript is part of the legacy Lua API which we will deprecate very soon. https://github.com/OpenRA/OpenRA/issues/5490