workflows: holdingpen updates

* Adds link to arXiv for arXiv identifiers.

* Shows only INSPIRE categories.

* Change the type of process_record_arxiv workflow
  from 'record' to 'Harvested record' to be distinguished
  from submitted records.

* Adds the type 'Submitted record' to literature and
  literature_simple workflows.

* Adds task halt_to_render to literature_simple workflow
  in order to update the title and description columns in holdingpen
  maintable.

Hmm, then there is something wrong with the cache invalidation. The workflow should already have refreshed itself after continuing the workflow on task `render_form`. It should use the timestamp now versus last modified of record. 

We need to make sure that the `last modified` are updated properly when the object is updated (should happen in obj.save())