Clarify how to use EditableInput without label
In the documentation for Editable input: 

> onChange - Function callback. Use this to call the onChange function of the parent. Returns an object where the key is the label and the value is the new value.

It is not clear what will happen if I don't provide a label. In 2.14 the onChange received the value instead of an object if no label was provided. I just upgraded to 2.17 and this behavior has changed, now I get `{undefined: value}`. Passing `null` as the label makes the onChange work like in 2.14.

I'm not sure if the change is a bug or it is intended, but it would be nice to have this documented.