jsonalchemy: fixes for versionable extension

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
documents: checker of source and uri addition

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
documents: test improvements

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
archiver: initial port to new code structure

Signed-off-by: Jake Cowton <jake.calum.cowton@cern.ch>
archiver: ...