elsevier_package: affiliation warning improvement

* Improves the warning of multiple implicit affiliations to
  not generate an error on concatenation.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
aps_package: XML format detection

* Adds support for simple XML detection in the APS converter. Raises
  new ApsPackageXMLError should the given XML be of a non-JATS format.

* For performance, ApsPackage allows client to pass pre-defined
  journal mappings.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
utils: new module for frequently used functions

* Moves function fix_journal_names to utils.

* Fixes function fix_journal_names.

* Adds function collapse_initials.

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