Don't include GLUT in mesh.h

We only need OpenGL itself

Signed-off-by: Casey Dahlin <cdahlin@redhat.com>
Port to GLFW

A much more sane and forward-compatible thing than GLUT. This should let us cut
down on the globals and move gradually toward a suite of visual tests rather
than a janky demo app.

Signed-off-by: Casey Dahlin <cdahlin@redhat.com>