Final Water Flow parts

Found a bug with plants removing water from the system. Now plants
remove water from the system and grow correctly, rain is handled
correctly, cross-farm flow is handled correctly (although right now it
just flows to opposite sides of the farm since the server stuff isn't up
yet), and internal water flow is handled correctly with an accuracy of 1
mL of water. I also added some variables at the top of my WaterFlow
class so that I can easily toggle plants and rain so that I can show the
model running with different things affecting it.