Move the binary installer background images to a new 'static' directory

Move the binary installer background images to a new 'static' directory at the root of the source code for containing miscellaneous static files that do not necessarily have to live directly in the root of the project.

I have been meaning to do this for a while, motivated in part from some comments in #1563 wherein the feeling was that the root of the project has become a bit too cluttered with miscellaneous files.  Some of those files have to be there since they're looked for by tools that expect to find them at a repository's root.  But any files that don't *have* to be there can be moved into 'static' or elsewhere.