private void BtnObrisiSatnicu_Click(object sender, RoutedEventArgs e)
        {
            int obrisan = k.obrisiSatnicu(dataGrid.SelectedItem as Satnica);

            if (obrisan == 0)
            {
                MessageBox.Show("Neuspesno obrisana satnica!");
                return;
            }
            else
            {
                MessageBox.Show("Uspesno obrisana satnica!");
            }
            dataGrid.ItemsSource = k.vratiListuSatnica();
        }