Added GameObjects and derivatives. Made minor window size changes.

Additions:
- GameObject class: base class from which all game objects will be
derived.
- Ball class: the brick breaking ball GameObject.
- Brick class: the class for the brick GameObjects that the Ball will
break.

Changes:
- Changed window width and height to allow up to 8 Bricks to fit in one
row.
- Removed the test bouncing ball.