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>
jsonalchemy: cache engine addition

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
travis: travis_retry statement for grunt

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