AMP Context state propagation

We can use [AmpContext](https://github.com/ampproject/amp-react-prototype/blob/104861c3777d5341377092620f123b9013c0050d/src/amp-context.js#L28) for all state properties such as `renderable` and `playable`. The main question is whether we breakdown the context per property or keep all the properties together. Breaking down per property means a lot of contexts, but also means fewer component updates.