deposit: authors placeholder and description change

Signed-off-by: Javier Martin Montull <javier.martin.montull@cern.ch>
deposit: fixes to MarcXML mapping

* Only other languages are added in 041, and they were abbreviated
  (before 041__a:ger, now 041__a:German)

* Journal title was missing in 773__p.

* No space between author initials (if abreviated).

* Adds the source to abstracts (for arxiv import e.g.: 520__9:arXiv).

* arXiv id in 037 was missing.

* Guesses 'page_nr' 300 field if isn't filled and has page_range field.

Signed-off-by: Pedro Gaudêncio <pedro.gaudencio@cern.ch>
deposit: arXiv field prefix

* Adds "$$9arXiv$$aoai:arXiv.org:" to the arXiv ID.

Signed-off-by: Pedro Gaudêncio <pedro.gaudencio@cern.ch>
deposit: file upload mapping

Signed-off-by: Pedro Gaudêncio <pedro.gaudencio@cern.ch>
deposit: updates CrossRef import fields mapping

* Updates the fields for the CrossRef Flask extension.

Signed-off-by: Pedro Gaudêncio <pedro.gaudencio@cern.ch>
deposit: 'status' key update

* Adapts to commits inveniosoftware/invenio#2024 and
  inveniosoftware/invenio@ffb60c3.

Signed-off-by: Pedro Gaudêncio <pedro.gaudencio@cern.ch>
base: enable Crossref extension

Signed-off-by: Javier Martin Montull <javier.martin.montull@cern.ch>