Android: Initial on-screen multitouch

Initial implementation of on-screen multitouch. I say initial because right now joysticks still will not work unless they are used by the first touch that enters the screen. I got rid of buttonState; it could not be used with multitouch since it could only hold the state of one button. This caused a revamp of that section of code.

This conflicts with #300; if it is merged before this I will rebase.