This commit includes
- new 'state' field on messages
- new permission on forum plugin (unmoderated_post)
- new moderation screen
- ability to set forum policy either to 'ApproveOnceModerated' or 'ModerateAll'.
If ApproveOnceModerated is set, then users with 'post' permission are
upgraded to unmoderated_post once they have a message approved
- ability to flag a message
- ability to remove/spam messages from moderation page