search: configuration of facets per collection

* Adds FacetCollection model with db upgrade.

Signed-off-by: Kamil Neczaj <kamil.neczaj@cern.ch>
Reviewed-by: Javier Martin Montull <javier.martin.montull@cern.ch>
search: flask-admin module to configure facets

* Adds Flask-Admin module available at /admin/facetcollection/.

Signed-off-by: Kamil Neczaj <kamil.neczaj@cern.ch>
Reviewed-by: Javier Martin Montull <javier.martin.montull@cern.ch>
search: facets relation definition move

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
global: Invenio 1.9999.4.dev

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