We no longer render animations as a base image with a
possibly-partially-transparent overlay drawn over it, so delete the
make-overlay.py tool. Now we represent them as series of images that
are interlaced by row (with a special text chunk in the PNG file
specifying the number of frames) so add the interlace-frames.py tool
to make those.
Change-Id: I79443f125f9c7d8d61cd09e3434745e0ef38893f
