Pep8/Aps harvest fixes.

* Fixes 999C5s field to always has the form of journal,volume,page.

* Adds basic metadata (pagecount, pacscode, author email,
  260__t:published, subjects)

* Removes arXiv prefix from the old format arXiv ids.

* Pep8 fixes and import refactoring.

* Moves format_arxiv_id into utils module.

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