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.
For subjects (65017) coming directly from arXiv we don't apply the translation. Leave the original, like ```65017 $$2arXiv$$ahep-th```

A different question is if we want to add an extra field with ```$$2INSPIRE``` where we add the translated version. In that case we need to check not to repeat what the user inputted in the form.