Find and add OCLC numbers once assigned

[rhigman]

We automatically check for new Thoth submissions going live on partner platforms (e.g. OAPEN) and then add their locations back into Thoth. In the same way, we should investigate the possibility of doing this with newly-assigned OCLC numbers.

WorldCat harvests Thoth metadata via pull and then assigns OCLC numbers on this basis.

Note that Project MUSE independently pulls in OCLC numbers and they are present in the metadata feed available for locations. An alternative option would be to use this as a source of OCLC numbers, but this would risk propagating third-party errors.