Allow for selectors to be used in DOMModel:getChildDOMModel / getChildDOMModelArray

[chrischrischris]

The recommended way of using RDC is to specify the custom components with nodeNames. However, in the DOMRegistry it's possible to use either a nodeName OR a selector that works with querySelectorAll (e.g: .className or #id)

However, that approach will not work with DOMModel:getChildDOMModel / getChildDOMModelArray. Both of those methods will only work with a nodeName.

This ticket is to add the ability to use query selectors when specifying the childDOM.