More work on rotation animation.

The black frame is now a separate animation element.  This allows us
to have it move through the aspect ratio change, without the old
and new screen elements doing weird aspect ratio scalings.  This
makes the animation generally look different (more like a reveal),
not sure if it is better or worse, but definitely has less artifacts
in things like the gallery.

Also tweaked the animation definitions a bit.

Change-Id: I94c274ba04bbc7a675946dc6c1778e19386e4a66