private void buttonUnRegister_Click(object sender, RoutedEventArgs e)
        {
            LetoviZaKartu z = new LetoviZaKartu();

            z.ShowDialog();
        }
        private void buttonKupiKartu_Click(object sender, RoutedEventArgs e)
        {
            LetoviZaKartu lzk = new LetoviZaKartu();

            lzk.ShowDialog();
        }