elsevier_package: fix dashes in report numbers

Signed-off-by: Georgios Papoutsakis<georgios.papoutsakis@cern.ch>
Merge pull request #34 from GiorgosPa/elsevier

elsevier_package: fix dashes in report numbers
pos_package: Fixes for PoS

* Adds 'PoS' classifier to the subjects.

* Removes field 500.

Reviewed-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
Signed-off-by: Georgios Papoutsakis <georgios.papoutsakis@cern.ch>