Created first draft of Player class + Changes

Created player class derived from GameObject class. Updated GameObject
class to include protected and virtual methods.
Added rectangle boxCollider to GameObject class

Added a rectangle to be used as a box collider. The box collider should
only be used in simple collisions i.e. making sure player doesn't walk
off screen.
Started outlining input handling

Created first draft of InputHandler class. Added functionallity to
Player class to store aim as a vector, and started creating method to
update the aim. Very minor code cleanup.