message: Fix CPU spin on joining large room
  checkIfAlone() filters the whole member list, which is fine until
  we do it once for every membership event, then we have an n^2
  problem. Move it into the rate limited function.
  Fixes
diff: @@ -701,7 +701,6 @@ module.exports = React.createClass({
  }
  this._updateRoomMembers();
  - this._checkIfAlone(this.state.room);
  },
  onRoomMemberMembership: function(ev, member, oldMembership) {
  @@ -717,6 +716,7 @@ module.exports = React.createClass({
  // refresh the conf call notification state
  this._updateConfCallNotification();
  this._updateDMState();
  + this._checkIfAlone(this.state.room);
  }, 500),
  _checkIfAlone: function(room) {
  