Update yum spider and download page for new reporpms

Update yum spider and download page for new reporpms

The yum project has switched to single-reporpm-for-multiple-versions as
well as putting them in a dedicated directory. This makes a lot of the
cruft in the code to deal with the distribution of reporpms unnecessary,
so change it.

We still need to keep track of which platforms exist for which versions,
so we do still need some spidering, but it's  alot simpler.

Since all versions are also always availeble, the javascript that
populates the version list can now just use the list of supported
versions. This could be rendered directly in the HTML, but we might need
to restrict versions-per-platform at some point in the future, and
javascript is needed anyway for the rest of the page, so we keep doing
it the old way.