WebSearch: quick checks in journal hint service

* Adds a quick `seems_a_journal_reference` function to the journal hint
  web service

* Adds unit tests for `seems_a_journal_reference`

Signed-off-by: Federico Poli <federico.poli@cern.ch>
Merge pull request #69 from fpoli/prod_websearch_journal_hint_quick_checks

WebSearch: quick checks in journal hint service