utils: arXiv identifier normalization

* Adds support for normalizing arxiv identifiers according
  to http://arxiv.org/help/arxiv_identifier and
  http://arxiv.org/help/arxiv_identifier_for_services.
  (closes #1958, #1961)

* Fixes issues with pre-2007 arxiv identifier validation.

* Fixes PEP257 problems.

* Adds tests including missing assertion of to_url() method.

Co-authored-by: Lars Holm Nielsen <lars.holm.nielsen@cern.ch>
Signed-off-by: Lars Holm Nielsen <lars.holm.nielsen@cern.ch>
editor: configuration fixes

* Moves config file out of legacy.

* Creates folder needed by BibEdit on app start.
  (closes #1965)

Signed-off-by: Javier Martin Montull <javier.martin.montull@cern.ch>
Reviewed-by: Lars Holm Nielsen <lars.holm.nielsen@cern.ch>
formatter: bfe_authors fix

* Fixes bibauthority configuration import issue.

Signed-off-by: Lars Holm Nielsen <lars.holm.nielsen@cern.ch>
Reviewed-by: Esteban J. G. Gabancho <esteban.gabancho@gmail.com>
formatter: bfe_authors pep8 fix

* Fixes PEP8 errors in bfe_authors. (closes #1962)

Signed-off-by: Lars Holm Nielsen <lars.holm.nielsen@cern.ch>
Reviewed-by: Esteban J. G. Gabancho <esteban.gabancho@gmail.com>