admin: administration menu fix

* Registers all subitems to the 'main.admin' menu item. (closes #1822)

Signed-off-by: Eirini Psallida <eirini.psallida@cern.ch>
installation: Flask-Assets 0.10

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
legacy: fix for imports and module renaming

* Adds several missing models for new tables.  (addresses #1790)

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

Signed-off-by: Yoan Blanc <yoan.blanc@cern.ch>