Brain.save_movie() II

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

True. Ignoring that warning, there are currently two ways of doing the same thing (mostly):

- specifying the montage when initializing the figure, and rendering frames from the whole figure
- initializing the figure with one or more views and specifying a montage that renders separate images from a single view in different orientations and then combines them to the individual movie frames

I wonder if it's worth supporting the latter then, since it means that any layout option basically requires two different implementations.