RefExtract: selective ref section title detection

* We now set a priority on which title form is the most important.
  References will be given priority over anything else while Reference
  will ranked last with Bibliography in between.
  That means that if "Bibliography" is found in the text, we assume it is
  the reference section and we don't look for a section titles "Reference".
PdfChecker: no arxiv queries on regression tests

* Mocks the query to arxiv that happened during regression tests.
Merge branch 'prod-arxiv-fixed' of https://github.com/Osso/invenio into replace-exact-author-tokenizer