Allow mining drills to support multiple output fluid boxes

[protocol_1903]

Since the minable properties of entities are a table of results, and since there can be multiple fluid results, you can encounter the case of a pumpjack type mining drill 'mining' multiple different fluids. In this case it only mines one fluid and ignores the rest. I would like mining drills to be able to mine multiple fluids at once, like with items. The best way to do this would be to specify multiple output fluidboxes for a single entity. Then, any entity with multiple fluid mining results can only be mined by an entity that has the required number of fluidboxes.