this ways we can keep the `lib/gitlab/ci/status/*` classes to return the
bare favicon name as it was before.
also the favicon uploader versions are now have the same names as the
stock favicons (+ `favicon_` prefix), which makes working with the
status names easier.
Without the '?' at the end of the favicon url the custom favicon (i.e.
the favicons that are served through `UploadController`) are not shown
in the browser. It may have something to do with how `#send_file` /
`#send_data` set http headers. When serving the same icon file from the
public directory everything is fine.
Alexis Reigel