protected T loadAdditionalAttributes(JsonObject jsonObject) {
		return null;
	}
Load additional attributes in the GUI.
Only needed if child class has additional elements which are not shown
in the parent class.
@param jsonObject 
@return default implementation: empty map
@see AsciidoctorConfigBase#load(Path, ActionEvent...)
src/main/java/com/kodedu/config/AsciidoctorConfigBase.java