FR: Add simpler DrawableButton constructor

I’m not sure about anybody else but I haven’t found a practical use for the button name when creating a DrawableButton. Can a constructor be added that looks like this?

    /** Creates a DrawableButton.

        After creating one of these, use setImages() to specify the drawables to use.

        @param buttonStyle    the layout to use

        @see ButtonStyle, setButtonStyle, setImages
    */
    DrawableButton (ButtonStyle buttonStyle);