message: Listened for native navigation in js Scene
  If navigate back on natie need to do the same navigation on js so that things are in step. If don't then fluent nav forward 2 and native back 1 then the scene would be blank because js thinks it's on a different crumb
diff: import React from 'react';
  -import {AppRegistry, NativeModules} from 'react-native';
  +import {AppRegistry, NativeEventEmitter, NativeModules} from 'react-native';
  import {NavigationContext} from 'navigation-react';
  class Scene extends React.Component {
  @@ -18,16 +18,26 @@ class Scene extends React.Component {
  }
  componentDidMount() {
  var {crumb, navigationEvent: {stateNavigator}} = this.props;
  - if (!crumb)
  + if (!crumb) {
  stateNavigator.onNavigate(this.handleNavigate);
  + var emitter = new NativeEventEmitter(NativeModules.NavigationMotion);
  + this.subscription = emitter.addListener('Navigated', ({crumb}) => {
  + var {stateNavigator} = this.props.navigationEvent;
  + var distance = stateNavigator.stateContext.crumbs.length - crumb;
  + if (distance > 0)
  + stateNavigator.navigateBack(distance);
  + })
  + }
  }
  shouldComponentUpdate(props, state) {
  return state.navigationEvent === props.navigationEvent;
  }
  componentWillUnmount() {
  var {crumb, navigationEvent: {stateNavigator}} = this.props;
  - if (!crumb)
  + if (!crumb) {
  stateNavigator.offNavigate(this.handleNavigate);
  + this.subscription.remove();
  + }
  }
  handleNavigate(_oldState, _state, _data, _asyncData, {crumbs}) {
  NativeModules.NavigationMotion.render(crumbs.length, AppRegistry.getAppKeys()[0]);
  