Allow the the ContentDisplay property and -fx-content-display to modify the layout of a RadioButton.

For example, the following should place the label radio underneath the radio button dot.
  new RadioButton("radio1").setContentDisplay(ContentDisplay.BOTTOM);
  new RadioButton("radio2").setStyle("-fx-content-display: bottom;");

Attached is a sample program and sample program output which demonstrates that the ContentDisplay property currently doesn't have much of an effect on a RadioButton.