Fix friends page to work with remote friends

Major changes:

    author/models:
        - getFriends, getPendingSentRequests, and
          getPendingReceivedRequests now return a dictionary with
          keys "local" and "remote", each containing a list of authors.

        - added RemoteAuthor, a foreign key to ReomteRelationship
            - this was needed to store information about remote authors
              other than their GUID (such as url and displayname, so
              they could be properly displayed on our local pages)

    RESTful API for friend stuff now work properly with GUIDs

    unit tests were updated to test for remote authors