Updated the Draw class to use OpenGL

Open GL is now used in the Draw class, and the Draw class now only
represents a single window.  2 instances of the draw class are now
needed for 2 windows, and you must draw to both of them.  Always make
sure your Draw window has context before trying to draw.
Merge pull request #21 from Amarcolina/DynamicShadowTech

Updated the Draw class to use OpenGL