added pub_status to article
added article type enum to article
validate pub status and article type according to enum values
working collab_author class related to article.  display on index page, update populate for rake....  NO TEST
added domains as many to many relationship to articles table with habtm.  domains are created in seeds.db.  use rake db:setup to both recreate the db and create the domains.  rake db:populate will add articles that refer to these domains.