WebSearch: new Journal Hint Service

* Adds the Journal Hint Service, that displays
  'Were you looking for a journal reference? Try: <link>'
  when the user search for a raw journal reference.

* Adds unit and regression tests for the new search service.

* Adds two unit tests to `search_from_reference`, just to be sure that
  it accepts unicode

Signed-off-by: Federico Poli <federico.poli@cern.ch>
Reviewed-by: Samuele Kaplun <samuele.kaplun@cern.ch>
Reviewed-by: Tibor Simko <tibor.simko@cern.ch>
WebSearch: smarter journal hint

* Improves the JournalHintService implementation by directly
  a brief representation of a record when one is found.

* Additionally, suggests to use find rawref "foo" when "foo"
  is searched for, rather than journal:"bar".
  (PR #1733)

Signed-off-by: Samuele Kaplun <samuele.kaplun@cern.ch>