search: facets per collection configuration

* Adds initial configuration with fixtures.

* NOTE to get facets shown
  invenio_demosite.base.fixtures.websearchh.FacetCollectionData needs
  to be loaded which means that you either need to recreate DB or
  load them manually.

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