Disallow non-members to join a MUC
Follow applications/hubl#906 (comment 56855)
Users who aren't member of a MUC should not get allowed to see its content, instead they should get a message telling them that they're not member of the circle and if they think that's an error they should contact an administrator.
I guess they'll be a converse part on it. I let you handle the eventual need of more specification and the token estimation @MattJ @manv