AppContainer binding: provide both a functor-based and a functor-less version

[cknitt]

• The functor-based version should be easier to use for beginners as it gives you a normal ReasonReact component (module). But it is not zero-cost.
• The non-functor-based version is zero-cost, but you need to do React.createElement(...) yourself. It allows advanced use cases such as (re)creating your AppContainer based e.g. on permission changes.

[MoOx]

This looks like a breaking change too right?

[cknitt]

Yes. We have only released an alpha so far, so I think that's alright.

The README is very outdated in any case, I will update it in a separate PR.