Fix Collision Detection

[ghost]

Current collision detection is kind of buggy. It only check if the objects are at the exact same x and y position (so if the edge of the sprite clearly touches the obstacle, the game doesn't register it as a collision.)

We will need to know the size of each obstacle and the runner in order to have a more accurate collision detection.

@andrewberls ~estimated 150

[jalexanderqed]

F16 CLOSED: Collision detection has been fixed.