message: Check if the message panel is at the end of the timeline on init
  Fixes
  componentDidUpdate is called a lot, and we don't really want to keep checking the messagePanel, so this introduces a new flag to check if the init is even needed.
diff: @@ -144,6 +144,7 @@ module.exports = React.createClass({
  // the end of the live timeline. It has the effect of hiding the
  // 'scroll to bottom' knob, among a couple of other things.
  atEndOfLiveTimeline: true,
  + atEndOfLiveTimelineInit: false, // used by componentDidUpdate to avoid unnecessary checks
  showTopUnreadMessagesBar: false,
  @@ -428,6 +429,12 @@ module.exports = React.createClass({
  roomView.addEventListener('dragend', this.onDragLeaveOrEnd);
  }
  }
  + if (this.refs.messagePanel && !this.state.atEndOfLiveTimelineInit) {
  + this.setState({
  + atEndOfLiveTimelineInit: true,
  + atEndOfLiveTimeline: this.refs.messagePanel.isAtEndOfLiveTimeline(),
  + });
  + }
  },
  componentWillUnmount: function() {
  