Author edit UI for entity_type to distinguish Corporate and Personal identities

On the tech mailing list, I wrote that searching authors for "museum" yielded 5608 results. By now, that number is 5614. I think it is time to provide a standardized way of saying authors are human or organization (or something else perhaps; a more general agent, a concept?).

Some author records have "entity_type" that may have been there to make the distinction, but there are many more values than "org" and "person" in use: https://gist.github.com/1895031#file_author_entity_type_choices.tsv
At the end of February 2012, there were 977 authors with such a entity type.

"entity_type" seems a good property to use, but it helps to agree on a minimal list of values and how to treat them in the HTML view and edit form. In the RDF view it can be used to choose between "foaf:Person" and "foaf:Organization" (or "foaf:Agent" if distinction cannot be made). I propose to use "org" for organizations/corporate identities and "person" for human authors and their pseudonyms.