private void BtnNew_Click(object sender, RoutedEventArgs e)
        {
            RentalDataEntry newWin = new RentalDataEntry();

            newWin.ShowDialog();
            UpdateList();
        }
        private void EditButton_Click(object sender, RoutedEventArgs e)
        {
            Button          button = sender as Button;
            Rental          rental = button.DataContext as Rental;
            int             index  = lvRentalList.Items.IndexOf(rental);
            RentalDataEntry win    = new RentalDataEntry(rental, false);

            win.ShowDialog();
            UpdateList(index);
        }