[core] Prepare the async API

[oliviertassinari]

• https://github.com/reactjs/rfcs/blob/master/text/0006-static-lifecycle-methods.md
• https://medium.com/@baphemot/whats-new-in-react-16-3-d2c9b7b6193b

[mbrookes]

Any chance of a couple of code comments so future maintainers know what's going on here?

[oliviertassinari]

@mbrookes It's far from being completed. It's 0.5% of the work needed. I think that the pull-request will grow to +1000 -1000 if not more. So yes, React changes will lead to profound changes here 🚧.

[nicholas-l]

Why not use react-lifecycles-compat instead of creating componentNew?

[oliviertassinari]

@nicholas-l I didn't know the project! Thanks for sharing.

[oliviertassinari]

This pull-request is half of the job done. We still have to migrate:

• componentWillUpdate x1
• componentWillReceiveProps x10

Let's ship this change to our users, and commit more effort if everything goes smoothly.