* Private forums: CanBeSeenBy moderators, approved followers, its owner and
admin users.
* Note: the endpoint to subscribe to the forum won't allow users to follow
the private forum, so approved followers can not be created at this time,
except by adding them as moderators.
* Admins: when creating a forum they can choose "no category" to create it as
an unofficial community forum.
* Code cleanup
* More feature flag checking
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