Refactor translator and editor support to accept lists

[JaimieMurdock]

Currently, translator and editor are just string fields, reflecting the project's roots in the BibTeX specification.

1. update the database author_of table
2. Update the pubs/model.py author_of table
3. Update the relationships on pubs.Citation
4. Update the pubssite/views.py PUT method to parse out translators and editors as well.