The logic is simplified by creating database rows for new mailboxes down
in Imapstore. This means that the difference between local and remote folder
lists are mailboxes that need to be deleted.
Note -- this is still not the final CL. We probably update the database too
frequently and the column values aren't updated to support nested folders.
Change-Id: Ifbe4e0cf74ba81e5b6156b452ab72c56c35235ab
200c6bd9fa