Handle duplicate authors

[willu47]

Despite improvements to the author checking and matching algorithm, which although simple does an effective job of matching authors, duplicates still appear from time to time.

A function to merge authors is required. This should:

• take the uuid of two duplicate authors
• merge fields of the two authors (or request input to select which fields to keep in the merged author profile)
• create a new author profile (or add :sameAs relation between them)
• update the :author_of relations so that they point to the merged author

Issues:

• external links to any deleted duplicate author would break if the author was deleted
• using :sameAs relations adds complexity to queries e.g. listing publications from an author AND any author which is :sameAs author