Added a few bubble acceleration changes.
Bubble.java- new function for acceleration factor, uses speed modifier.
MyGdxGame.java- look for yourself; the position change is now defined by a quadratic function.
Working- The bubbles now accelerate randomly and are pretty trippy. This does not include the exponential function addition.
Bugs- The bubbles often spawn in one part of the screen, but the random acceleration causes it to move toward the same side, thus taking it off screen before the user has a chance to touch it.