Brain.save_movie() II

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

I think I'd prefer it not be there at all for now. I imagine it simplifies the code quite a bit to say it animates the current view(s), and also makes an easy explanation for users: change your `Brain` view to what you want to create a movie of. I'd rather expand the options for making more flexible `Brain` view setting/manipulation than have it be handled piecewise by functions. There are already functions that do such piecewise handling, but IIRC they existed before you could set multiple views simultaneously.