message: use JumpToBottomButton in RoomView
diff: @@ -1861,6 +1861,14 @@ module.exports = React.createClass({
  onCloseClick={this.forgetReadMarker}
  />);
  }
  + let jumpToBottom;
  + if (!this.state.atEndOfLiveTimeline) {
  + const JumpToBottomButton = sdk.getComponent('rooms.JumpToBottomButton');
  + jumpToBottom = (<JumpToBottomButton
  + numUnreadMessages={this.state.numUnreadMessages}
  + onScrollToBottomClick={this.jumpToLiveTimeline}
  + />);
  + }
  const statusBarAreaClass = classNames(
  "mx_RoomView_statusArea",
  {
  @@ -1898,6 +1906,7 @@ module.exports = React.createClass({
  { auxPanel }
  <div className="mx_RoomView_timeline">
  { topUnreadMessagesBar }
  + { jumpToBottom }
  { messagePanel }
  { searchResultsPanel }
  </div>
  