Added ClonesProductionUnits trait for RA2-style Cloning Vats

Yep we're in a feature freeze.
Yep we don't have RA2 yet.

I think mod authors will be happy to have this a few games early.
`self.World.ActorsWithTrait<ClonesProducedUnits>().Where(a = a.Actor.Owner == self.Owner)` would be more efficient.