extra arXiv mapping

Add extra fields from arxiv (same as in oaiharvest) to the form fields (see [asana task](https://app.asana.com/0/8772567966361/12984151070479)).

arXiv journal names mapping depends on https://github.com/jmartinm/inspire-next/commits/overlay-changes.
It should be ```oai:arXiv.org:``` instead of ```aoai:arXiv.org:```