message: Retained scenes onNavigate
  Always want the latest scene data, not the one at time of last render.
  So need to keep track of it instead of leaving it up to TransitionMotion
diff: @@ -5,21 +5,10 @@ import { View } from 'react-native';
  import spring from './spring.js'
  class NavigationMotion extends React.Component<any, any> {
  - private onNavigate = (oldState, state, data) => {
  - this.setState((prevState) => {
  - var scenes = {};
  - var previousScene = null;
  - var {url, crumbs} = this.getStateNavigator().stateContext;
  - for(var i = 0; i < crumbs.length; i++)
  - scenes[crumbs[i].url] = previousScene = prevState.scenes[crumbs[i].url];
  - var element = state.renderScene(data, this.moveScene(url), previousScene && previousScene.data);
  - scenes[url] = {...prevState.scenes[url], element};
  - return {scenes};
  - });
  - }
  constructor(props, context) {
  super(props, context);
  this.state = {scenes: {}};
  + this.onNavigate = this.onNavigate.bind(this);
  }
  static contextTypes = {
  stateNavigator: React.PropTypes.object
  @@ -37,15 +26,24 @@ class NavigationMotion extends React.Component<any, any> {
  componentWillUnmount() {
  this.getStateNavigator().offNavigate(this.onNavigate);
  }
  + onNavigate(oldState, state, data) {
  + this.setState((prevState) => {
  + var scenes = {...prevState.scenes};
  + var {url, crumbs} = this.getStateNavigator().stateContext;
  + var previousScene = crumbs.length > 0 ? prevState.scenes[crumbs[crumbs.length - 1].url] : null;
  + var element = state.renderScene(data, this.moveScene(url), previousScene && previousScene.data);
  + scenes[url] = {...scenes[url], element};
  + return {scenes};
  + });
  + }
  moveScene(url) {
  return data => {
  this.setState((prevState) => {
  var scenes = {...prevState.scenes};
  - if (scenes[url])
  - scenes[url].data = data;
  + scenes[url] = {...scenes[url], data};
  return {scenes};
  - }
  - )};
  + });
  + };
  }
  getScenes(){
  var {crumbs, nextCrumb} = this.getStateNavigator().stateContext;
  