Added the OreStack class

The OreStack class is for mod recipes that support stack sizes larger
than 1, and I think that it would be convenient to have that in forge.
Instead of registering each OreDictionary name as a separate ItemStack, you just use the OreStack in recipes like the Ic2 Macerator or the RP2 Alloy furnace, that currently seem to use the multiple ItemStacks method (Checked with NEI's recipe viewing feature).

p.s.: I'm bad at explanations.