Brain.save_movie() II

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

Hm, I added the `row` and `col` params based on other methods, but is it really necessary to expose them? The only corner case I can think of is when the user manually rotates the brain in a view other than the bottom right and then wants to take a movie of it. All other possibilities could be specified with the montage parameter. We could leave row and col for now (just use the default) and add them if a use case comes up?