Add a lose condition if the player falls below screen height

This just exits the game for now.
Update creation of platforms

This will now create better platforms for running and jumping on.
Update Runner model

Added a speed variable and removed friction from box2d body.
Update default friction and restitution values
Change platforms to Vector

The Vector class is better suited for how the platforms need to be
handled.  It allows objects to be removed and added at will.