[testsuite] add some basic checks for generated repomd data.

This will allow us to include createrepo into our testing to avoid broken repositories
in future. We need to hard require the tested version of it then in the obs-server package.
[backend] also restore the signkey when undeleting a project
[webui] set expire date for avatar icons
[webui] disable miniprofiler by default - it disables caching
[webui] replace more images with sprites
[api] move release_package function to helper
[api] drop obsolete check of releasetargets, but fix update of release trigger mode instead
[api] support manual package release according to Fate #315081

This requires that the repository release target is defined and the trigger is set to "manual".
Comes with some cleanups of code
[api] support release of entire project
[backend][api] move daemon states of /build/_workerstatus into daemons element for each sibling