Control call to setFocusTraversable make it so focusTraversable cannot be set on a Control via css

Obscure little bug, but this code causes a flag to be set on focusTraversable that indicates the property was set by the user, which means it won't get overriden by css.

    protected Control() {
        setFocusTraversable(true);
    }

The property should be initialized like so.

    protected Control() {
        StyleableProperty prop = StyleableProperty.getStyleableProperty(focusTraversableProperty());
        prop.set(this, true, null);
    }