message: Changed way ensure history added only once
  The previousState is only null on first load so makes the ideal candidate to use instead of separate historyAdded var
diff: @@ -8,19 +8,17 @@ import Photo from './Photo';
  import {getHome, getTweet, getTimeline} from './data';
  export default () => {
  -
  - var historyAdded = false;
  const historyManager = new MobileHistoryManager(url => {
  - var {state, data} = stateNavigator.parseLink(url);
  + const {state, data} = stateNavigator.parseLink(url);
  + const {previousState} = stateNavigator.stateContext;
  var fluent = stateNavigator.fluent().navigate('home');
  - if (!historyAdded)
  + if (!previousState)
  stateNavigator.historyManager.addHistory(fluent.url, true);
  if (state.key === 'photo') {
  fluent = fluent.navigate('tweet', {id: data.id});
  - if (!historyAdded)
  + if (!previousState)
  stateNavigator.historyManager.addHistory(fluent.url);
  }
  - historyAdded = true;
  return fluent.navigate(state.key, data).url;
  });
  