Add comment/thread/review approval system

[rubenwardy]

• "Comments" includes comments, new threads, and new reviews.
• Comments should have an approved field. If approved=false, then it should only be visible to the author and moderators.
• New members that post a link should have approved=false.
• Perhaps a filter list that requires approval for comments that contain hate keywords. Trusted Members would be exempt.
• Otherwise, comments approved by default.

[wsor4035]

a quick win would be the ability to make a current thread private, as currently threads can only be deleted