Refactored, changed dt, fixed bugs?

Changed the delta time to be based on actual values, rather than a fixed
value (wouldn't inherently be correct).
Also (hopefully) fixed the bug where at higher speeds, the ball flies
through the paddle. Not 100% sure though because I'm not good enough at
pong to test it out.

Also, for now, we are still being inefficient using js mouse events
because Animatron's is still buggy.
Improved ball movement, added support for AI and created two AIs, a perfect one, and one that errors a little and has speed limiting. Reference ai_human.js for a good template for creating an AI. To use your own, include it and change the constructor name to your AI name. (This hopefully will be done through the UI in the future).