OpenGL Support.
 - Added OpenGL to XCode Project.
 - Updated GameWindow to use OpenGL.
 - Updated main to run even if window is closed (for OpenGL shutdown).

Overhauled GameWindow
 - Added Getters and Setters.
 - Fixed window initialization.
 - Moved code to .cpp.
 - GameWindow closes itself.

Removed #import <string> as it was not needed.
Formatting.