private void Add_Click(object sender, RoutedEventArgs e)
 {
     AddCustomer customerAddingScreen = new AddCustomer();
     customerAddingScreen.ShowDialog();
 }
 private void buttonAddCustomer_Click(object sender, RoutedEventArgs e)
 {
     AddCustomer addCustomerWindow = new AddCustomer();
     addCustomerWindow.ShowDialog();
 }