private void DodajUKorpu_Click(object sender, RoutedEventArgs e)
 {
     if (IzabraniIndex >= 0 && IzabraniIndex < ListaKupovine.Count)
     {
         ListaKupovine.RemoveAt(IzabraniIndex);
         IzabraniIndex = -1;
         Refresh();
         Sumiraj();
     }
 }
 private void Odustani_Click(object sender, RoutedEventArgs e)
 {
     ListaKupovine.Clear();
     this.Close();
 }