arxiv: OAI2 API usage and status code addition
- Changes the arXiv import source to OAI2 url. (addresses #1866)
- Adds status code to API request.
- Updates existing unit tests and adds new ones: unsupported versioning and malformed.
- It's able to get more info than before.
Signed-off-by: Pedro Gaudêncio <pedro.gaudencio@cern.ch>
Reviewed-by: Jiri Kuncar <jiri.kuncar@cern.ch>