edpsciences_package: convertion fixes

* Adds 980__a:ConferencePaper.

* Adds reference numbers.

* Adds licence harvesting.

* Removes footnotes from title and places
  them to 500__a field. Adds subtitle harvesting.

* Adds subject harvesting.

* Adds keywords harvesting.

* Adds harvesting of article type and only converts articles
  with types 'research-article', 'introduction', 'letter'.

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