private void Save_Click_Button(object sender, RoutedEventArgs e)
        {
            if (NameTextBox.Text == String.Empty || SurnameTextBox.Text == String.Empty || LoginTextBox.Text == String.Empty || PasswordTextBox.Text == String.Empty)
            {
                MessageBox.Show("Uzupełnij puste pola!");
                return;
            }
            Courier us = null;

            try
            {
                us = DB.CouriersList.Where(u => u.Login == LoginTextBox.Text).Single();
            }
            catch (Exception) { }
            if (us != null && css.Login != LoginTextBox.Text)
            {
                MessageBox.Show("Podany login jest zajety!");
                return;
            }
            BindingExpression binding = NameTextBox.GetBindingExpression(TextBox.TextProperty);

            binding.UpdateSource();
            binding = SurnameTextBox.GetBindingExpression(TextBox.TextProperty);
            binding.UpdateSource();
            binding = PasswordTextBox.GetBindingExpression(TextBox.TextProperty);
            binding.UpdateSource();
            binding = LoginTextBox.GetBindingExpression(TextBox.TextProperty);
            binding.UpdateSource();
            MessageBox.Show("Aktualizacja danych powiodła się!");
        }