global: PEP8 fixes and import refactoring.

Singed-off-by: Georgios Papoutsakis<georgios.papoutsakis@cern.ch>
minidom: Moves format_arxiv_id into utils module

* Removes arXiv prefix from the old formated arXiv ids.

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

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

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

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