MUC: Allow kicking users with the same affiliation as the kicker (fixes #1724) This is allowed by XEP-0045, which states: "A moderator SHOULD NOT be allowed to revoke moderation privileges from someone with a higher affiliation than themselves (i.e., an unaffiliated moderator SHOULD NOT be allowed to revoke moderation privileges from an admin or an owner, and an admin SHOULD NOT be allowed to revoke moderation privileges from an owner)."