Retraction papers

[xuanxu]

This PR adds the ability to create retraction notices and retract papers using the API.

[xuanxu]

Run migrations after merging

[arfon]

@xuanxu – @chartgerink is looking to better understand how all of this works (for our PMC submission). Is this a good summary?

Essentially we now:

• Publish a new short retraction paper (authors are the 'JOSS editorial team' or whatever/whomever we want them to be').
• Link the retraction notice paper back to the original (retracted) paper.
• Mark the original paper as retracted in the JOSS UI (and link to the retraction notice).

I think that's about it right? Are there other things that happen in the Crossref metadata?

[xuanxu]

Yeah, that's it.
The retraction paper is deposited with Crossref as any other paper, no extra special metadata.