BibTasklets: add back old date detection

* Adds back the old threshold date detection in the APS harvester
  as a fallback from the new date detection, should the downloaded
  XML be in the old format.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
Bibcheck: Adds a temporary plugin

* Corrects the authors from some old atlas papers

Signed-off-by: Georgios Papoutsakis <georgios.papoutsakis@cern.ch>
BibCheck: adds a new plugin and unit tests

* Adds journal_names plugin.

* Adds unit tests for the new plugin and
  atlas_authors plugin.

* Fixes pep8 issues on atlas_authors.

Signed-off by: Georgios Papoutsakis <georgios.papoutsakis@cern.ch>