Feature tilt bounce improvements

This branch implements all the tilt and bounce revisions outlined in our [11/23/14 meeting notes](https://github.com/zsweedyk/CS121F14S4_Team5/wiki/Meeting-Notes,-11.23.14) *except* that it does not play a sound effect when an object hits the pipe bar. I haven't yet done that because I couldn't figure out how to detect those collisions.