Allow users to be banished from Conpherence rooms

Summary: Fixes T9348. If you have edit permission, you can kick people out of a room.

Test Plan:

• Kicked people out of a room.
• As an unprivileged user, wasn't able to kick people out of a room.
• Hit most (all?) of the various weird dialog sub-cases.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9348

Differential Revision: https://secure.phabricator.com/D15728