Remove window buttons

I have extended Undecorator to allow the user to remove the window buttons.  I have moved all the code for handling the window buttons to ButtonController.java.  If the user passes in null for the stageDecorationFxml parameter in the constructor, than the ButtonController will not be instantiated and so those associated fxml components will not be added to the screen.

Thank you for developing Undecorator, I am now using it in my project Keyboarding Master.