Redo the base gif files. These are very simple; just a lot of white

in the right size. Wow, we could probably even generate this image on
the fly, except that it has that nice little directional legend that Tim
added, and I don't want to mess with that right now!

Note that the new floormap code will draw all the obstacles, even the
walls, so there is not need for anything in the base gif anymore.