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.
If the `title_arXiv` is present, this means that the data was imported from arXiv...Perhaps setting up some hidden checkboxes like `imported_from_arxiv` and `imported_from_crossref` and check them when the data is imported would be a better solution. I just took the title because it would be a field that by all means would be provided by arXiv.