search: facets per collection

Allows to configure independently facets for every collection

Flask-Admin module available at /admin/facetcollection/

Matching fixtures for demosite: https://github.com/inveniosoftware/invenio-demosite/pull/21
Adaptation for inspire: https://github.com/inspirehep/inspire-next/pull/21

There is no need to recreate DB. The facets added to the default collection with id '1' will be displayed in other collections which doesn't have the facets set defined.

You need to run the updater to update your DB.

Alters: https://github.com/jirikuncar/invenio/pull/242
In the upgrade recipe you could add a note like https://github.com/inveniosoftware/invenio/blob/pu/invenio/modules/upgrader/upgrades/invenio_2013_03_20_idxINDEX_synonym_kb.py#L53

To tell the user that for facets to appear they need to first be configured in /admin. Otherwise you run the upgrade and there is a blank space close to the search results without much information about where to configure them