Tutorial: YouTube card events.

One can send events from the playground via:
```js
Playground.conductor.cards['../cards/tutorial/youtube_card.js'][1][0].sandbox.videoPort.send('play');

// we add the video port to the window for convenience in the tutorial
window.videoPort.send('play');
```
Tutorial: Child cards.

```js
Playground.conductor.cards['../cards/tutorial/ad_card.js'][1][0].sandbox.videoPort.send('play');

// we add videoPort to window for convenience in the tutorial
window.videoPort.send('play');
```
Tutorial: Update child card data.
Tutorial: Respond to data changes.