message: Added prop to unshare the element
  No need to unregister immediately when props change because register
  called on navigate
diff: @@ -26,10 +26,14 @@ class SharedElement extends React.Component {
  var {url} = this.state;
  if (url === this.getStateNavigator().stateContext.url
  || url === this.getStateNavigator().stateContext.oldUrl) {
  + var {unshare, name, data} = this.props;
  + if (!unshare) {
  this.ref.measure((ox, oy, w, h, x, y) => {
  - var {name, data} = this.props;
  this.context.registerSharedElement(url, name, this.ref, {w, h, x, y}, data);
  });
  + } else {
  + this.context.unregisterSharedElement(url, name);
  + }
  }
  }
  render() {
  