Fluid Settling (0.16.0 Alpha)

The big new feature of this release is fluid settling.  It used to be that whenever you had large amounts of fluid on screen, even if it wasn't moving, it consumed processor time.  Now, fluids only consume processor time when they're in motion.  It's not as efficient as I'd like, but I will try to improve on this.

Additionally, I fixed some pretty big bugs involving actors with sensor fields (Attraction Balls) interacting incorrectly with platforms and fluids.

There are also a number of internal code changes for the sake of readability, mostly involving the FluidHandler.