message: Refactored into contextStyle
  More consistent with willEnter and willLeave
diff: @@ -45,10 +45,10 @@ class NavigationMotion extends React.Component {
  }
  )};
  }
  - calculateStyle(scene, mount, state, data) {
  + contextStyle(scene, url) {
  var {mountedStyle, crumbStyle} = this.props;
  - var style = (scene && scene.style) || (mount ? mountedStyle : crumbStyle);
  - return getStyle(style, state, data);
  + var mount = url === this.getStateNavigator().stateContext.nextCrumb.url;
  + return (scene && scene.style) || (mount ? mountedStyle : crumbStyle);
  }
  render() {
  var {state, data, crumbs, nextCrumb} = this.getStateNavigator().stateContext;
  @@ -61,7 +61,7 @@ class NavigationMotion extends React.Component {
  styles={sceneContexts.map(({state, data, url}) => ({
  key: url,
  data: {scene: this.state.scenes[url], state, data},
  - style: this.calculateStyle(this.state.scenes[url], url === nextCrumb.url, state, data)
  + style: getStyle(this.contextStyle(this.state.scenes[url], url), state, data)
  }))}>
  {tweenStyles => (
  <div style={style}>
  