moved Mesh OpenGL methods to Scene.
finished moving Mesh.draw() to Scene.draw().  Noticed that shadow rendering isn't working properly again.
minor fixes
fixed cubemap bug.  Added back conditional glViewport call.
fixed shadow rendering bug by removing the glOrtho code.  No longer need text rendering, will use Qt for that.
deleted pyglet.resource import from mesh.py
removed feature for mesh to copy texture file through Mesh.load_texture, in order to do code cleaning (I never use that feature anyway)
fixed merge conflict with mesh branch