[webui] Show request priorities
[webui] Get rid of /user/requests/ in html
[backend] do not come with a download_url in backend config anymore by default

we have by default a different config in /configuration which breaks test suite
[api] just switch order of migration steps

It is one big transaction and people are confused not to see
changes, when the warning of not converted entries pops up in the middle.
[doc] explain priority meanings
[backend] publish all install.tbz and tgz kiwi images
[api][webui] use download url's as reported by the backend

Otherwise the download might break on special mappings