deposit: fixes to fillform arXiv import

* Updates fields regarding the new OAI2 import API.

Signed-off-by: Pedro Gaudêncio <pedro.gaudencio@cern.ch>
deposit: note and arXiv comments hidden fields

* Adds the note hidden field and imports arXiv comments field onto it.

Signed-off-by: Pedro Gaudêncio <pedro.gaudencio@cern.ch>
deposit: proceedings info removal if published

* Removes nonpublic_note key from metadata (500__a) if any of the
  publication fields are filled.

Signed-off-by: Pedro Gaudêncio <pedro.gaudencio@cern.ch>
deposit: addition of license url hidden field

* Adds license url field if it's present in arXiv import.

Signed-off-by: Pedro Gaudêncio <pedro.gaudencio@cern.ch>