Supporting refs for internal and external use

[jamesplease]

Presently, there is a divide of sorts when it comes to Materialish refs. If a ref is used internally, then it cannot be used externally. And vice versa.

There are only a few situations when refs are needed internally. But those components do not have a nodeRef prop.

@conorhastings proposed a solution to this in #267 (comment) (CodeSandbox Example).

There is a catch: it doesn't support string refs. But that may okay, given the benefits that this API provides, and the fact that string refs are deprecated.

[conorhastings]

thinking further about this, not allowing string refs seems especially fine since the prop is nodeRef, they would actually have direct access via this.refs['string'] they would have to attach a direct ref to the materialish node and use this.refs['something'].children.refs['string']

I think calling out lack of support for string refs in nodeRef in docs seems appropriate since above workflow is really poor anyway

[jamesplease]

Over in #240 , this would be pretty useful to enable us to refocus the input after the clearable button is clicked.

[jamesplease]

Here is what I'm thinking:

getRef = ref => {
  const { nodeRef } = this.props;

  if (typeof nodeRef === 'function') {
    nodeRef(ref);
  } else if (nodeRef && nodeRef.hasOwnProperty('current')) {
    nodeRef.current = ref;
  }

  this.nodeRef = ref;
}

[jamesplease]

Resolved in #277 . This will be released as 0.17.0; possibly tonight or tomorrow. I'm just doing a bit more testing to make sure that everything is good.