WebSearch: configurable viewrestrcoll policy

• The default policy when a record belongs to more than one restricted collection is to grant access only to users authorized to *all* these restricted collections. By setting the new config variable CFG_WEBSEARCH_VIEWRESTRCOLL_POLICY in invenio-local.conf to "any", an administrator can now change this policy and can grant access to users that are authorized to at least one of these restricted collections.