Admin interface to split/join Works

[leonardr]

Moved from https://github.com/NYPL-Simplified/content_server/issues/75.

Sometimes different books have exactly the same title and author. This is the only example I can find but it's pretty important and there are probably others:

http://www.gutenberg.org/ebooks/author/3906

It probably happens more often for books with institutional authors.

When two books have exactly the same title and author, they end up with the same permanent work ID, and if the books are both open-access books, they're grouped together. Most of the time this is correct, but not here.

A human being can determine that the books are different, but there is no way for a human to see the different works that are joined together, or to split apart works that have been wrongfully joined. We also have no way of tracking this information, so that we don't immediately 'notice' that two works with the same permanent work ID have somehow become un-joined and join them right back up.

[aslagle]

In addition, when two open-access books are joined into the same work, an admin should be able to pick which edition to use.