improve author handling on hathi import

[rlskoeser]

Would like to move authors (or possibly all creators, if we add editors & translators) out of a text field into a related table so we can group and manage records better.

Peter Green suggests using the 'known label retrieval' from LOC - https://id.loc.gov/techcenter/searching.html . I checked, if we remove the trailing period this is working for the sample records we tried.

This means:

• add a new person model (name, uri; notes?) and replace author text field with a many-to-many
• update hathi import to find existing or add new author record
• use LOC known label retrieval to look for LOC URI and add to the database
• update Solr indexing to handle change to author field
• update CSV export to handle change to include author name and URI

[mnaydan]

We decided to do this outside of the database.