Brain.save_movie() II

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

What I meant is that if you have the number 60 in your head, that is probably because NTSC standard contains 60 half frames. I was not suggesting using that when saving movies. I would just use 25 FPS because that is enough for fluid perception and uses less space.