Show slots for each item when multiple are needed during crafting (i.e. leather)

Right now if you are making an item and it calls for two (or more) of something, you have to have all of them identical. If I have several leather, but each used something different, I can't use that to craft something that needs two leather. If we had separate slots for each we could do that. It would also eliminate a whole lot of extra slots needed for storage.