private void AddNewCustomer_Click(object sender, RoutedEventArgs e)
 {
     AddNewCustomerWindow addCustomer = new AddNewCustomerWindow();
     addCustomer.ShowDialog(); 
 }
 //Customer Management ###################################################################################################
 
 //Button Add New Customer
 private void button_ClickAddNewCustomer(object sender, RoutedEventArgs e)
 {
     AddNewCustomerWindow newCustomer = new AddNewCustomerWindow();
     newCustomer.ShowDialog();
 }