Keep reference to real synthetic input component

[Deraen]

To implement proper on-update function for React input wrapper components, reference to the real component is probably needed.

Discussion at madvas/cljs-react-material-ui#17
Example at https://github.com/Deraen/problems/blob/reagent-material-ui-text-field/src/hello_world/core.cljs#L16

[Deraen]

I've been looking to finalizing this, but seems like this approach can't work with material-ui 1.0 as ref can't be used with new TextField which is implemented as Functional Stateless Component. This means it is impossible to get access to the React component.

I'm starting to think it will be near impossible to fix this until React starts supporting async rendering (could be soon: https://reactjs.org/blog/2018/03/27/update-on-async-rendering.html).

I'll keep thinking about this and if I find solution, before I'll merge it or release 0.8 I'll add examples for Material-UI, both 0.20 and 1.0-beta and React-bootstrap so we can be sure the approach works for different cases.

If I don't find solution, I'll likely revert the current synthetic-input code before release, as I think it is broken and will just cause confusion.

[Deraen]

Proper solution has been found for v1: https://github.com/reagent-project/reagent/blob/master/examples/material-ui/src/example/core.cljs