public static object ShowPopUp(AirportContract contract)
        {
            PopUpWindow window = new PopUpAirportContract(contract);

            window.ShowDialog();

            return(window.Selected);
        }
        public static object ShowPopUp(AirportContract contract)
        {
            PopUpWindow window = new PopUpAirportContract(contract);
            window.ShowDialog();

            return window.Selected;
        }