Add a basic scene with gravity and a ball node

Gravity can be changed by tapping, sliding, and releasing a finger. The
vector representing the acceleration rate and direction of gravity is
computed by finding the deltas between the touch down and touch up
events (no flicking, swiping, etc.).
Create .gitignore
Create README.md
Surround the ball by squares & use motion controls
Play music notes on collision
Fix crash when backgrounded