/// <summary>
/// Saves user in database and clear all fields after click "Zapisz" ["Save"].
/// </summary>
private void SaveButton(object sender, RoutedEventArgs e)
{
CreateUser.AddClientToDatabase(userNameTextField.Text, userSurnameTextField.Text, passwordTextField.Text);
userNameTextField.Clear();
userSurnameTextField.Clear();
passwordTextField.Clear();
}