Correctly handle order_quantity for finished product

[LarrySnyder]

Currently, _raw_materials_to_finished_goods() loops through products and processes as many units as possible for each. This means if there are two FGs that use the same RM, all units of the RM will be used to make the first FG.

The fix has to be some way of keeping track of "orders" of the FG, not only the RM.

[LarrySnyder]

Fixed in 45540be