Inspire next facets per collection

Allows to configure independently facets for every collection

Flask-Admin module available at /admin/facetcollectionview/

Matching fixtures for demosite: https://github.com/inveniosoftware/invenio-demosite/pull/21

There is no need to recreate DB. Instead of loading the fixtures - which are the default configuration, you can add facets by the Flask-Admin module. The facets added to the default collection with id '1' will be displayed in other collections which doesn't have the facets set defined.

Alters: https://github.com/jirikuncar/invenio/pull/242
GVR has always been [against abusing map/lambda](http://www.artima.com/weblogs/viewpost.jsp?thread=98196) when comprehension lists were doing the same.

```python
return [facet.get_conf(collection=collection, qid=qid) for facet in facets_set]
```