Brain.save_movie() II

Alternative to https://github.com/nipy/PySurfer/pull/79 co-opting `Brain.make_montage()`

Tmin and tmax is fine with me, I already changed it, I just had start and stop originally based on python slicing. I would specify framerate in FPS, seems more natural to me, probably from movie processing, do you prefer duration of the frame?