[REVIEW] Make controller instantiation customizable

[Greg Brown]

> Having <?param?> allow multiple arguments to this constructor of object represented by FXML. 

OK. How you might expect to use this feature in practice? I.e. what arguments might you want to pass to the FXML? How would you expect to pass them? How would you expect them to be used/accessed by the document and/or its associated logic? A simple use case with sample pseduo-code would be very helpful.

Thanks,
Greg