message: Fix docs & add MatrixClient check
  Addresses PR feedback without breaking RoomSettings
diff: @@ -38,7 +38,7 @@ function parseIntWithDefault(val, def) {
  const BannedUser = React.createClass({
  propTypes: {
  - member: React.PropTypes.string.isRequired,
  + member: React.PropTypes.object.isRequired, // js-sdk RoomMember
  },
  _onUnbanClick: function() {
  @@ -147,7 +147,10 @@ module.exports = React.createClass({
  componentWillUnmount: function() {
  ScalarMessaging.stopListening();
  - MatrixClientPeg.get().removeListener("RoomMember.membership", this._onRoomMemberMembership);
  + const cli = MatrixClientPeg.get();
  + if (cli) {
  + cli.removeListener("RoomMember.membership", this._onRoomMemberMembership);
  + }
  dis.dispatch({
  action: 'ui_opacity',
  