[0.79] Add the ability to drain water from a barrel directly into a water jug

This will allow players to right click a barrel with a water jug or place the jug in the barrel fill slot to fill the water jug.

An important thing to note here is I did *not* register the waterjug as a fluid container for one important reason:
Any item registered as a fluid container can be both filled and drained into the barrel, but now that we have finite water in 0.79, and water jugs can pick up water without removing source blocks it would be a very very cheap way to produce large quantities of water very fast.  I also figured that dumping your water jug into the shared water supply was unsanitary :)

So water jugs are half a bucket worth of water and can only pull water out of a barrel, not put water in.