@Override
    public boolean getState() {
        return isOn;
    }
@param onPreset  The face to display when in the ON state, e.g. an OFF icon
@param offPreset The face to display when in the OFF state, e.g. an ON icon
stroom-core-client-widget/src/main/java/stroom/widget/button/client/SvgToggleButton.java