search: loading of Bloodhound using requirejs

* Adds the missing export of twitter's typeahead.js and properly
  loads it with requirejs at search typeahead.

Signed-off-by: Kamil Neczaj <kamil.neczaj@cern.ch>
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>