Conflicts:
	pronterface.py

This callback is useful to broadcast the last print line sent in the form of
the parsed gcoder.Line object. We can then augment the gcoder.Line to do
awesome stuff, such as updating the print status in the 3D viewer.

This commit introduces a use3dview flag, which will be made as an option as
soon as we get a better options GUI.

Several small modifications were required, such as providing build dimensions,
adding some flags, translating numpy arrays into pyglet VBOs and using the
right pyglet GL API function names.

This allows the white background to show through the Graph,
fixing the background problem in #359

@iXce's change in 94d69f79 was on the right track, but
has to occur earlier in the draw cycle.