WebStyle: more accurate "Restricted" flag display

* Rely on search_engine.get_restricted_collections_for_recid(..)
  and search_engine.is_record_in_any_collection(..) in order to
  test if restricted flag should be displayed or not, instead of
  search_engine.record_public_p(..). It avoids displaying the
  flag when the record belong to a collection not directly
  searchable from the home collection. It allows to display
  an alternative flag when the record has not been fully
  integrated (not linked to any collection). It also display
  the restricted flag on record belonging to both a restricted
  collection and a public collection searchable from the home
  tree. (addresses #867)

* Added regression test for record belonging to both a public
  and a restricted collection.

Reviewed-by: Tibor Simko <tibor.simko@cern.ch>