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.
Would it be better if `produced` was the `ActorInfo` instead of the actor itself? I don't think this trait needs to have access to the actual instance.