private void buttonCustomerManagement_Click(object sender, RoutedEventArgs e)
        {
            CustomerListWindow listWindow = new CustomerListWindow();

            listWindow.ShowDialog(); 
        }
        private void CustMgmtList_Click(object sender, RoutedEventArgs e)
        {
            CustomerListWindow customerlist = new CustomerListWindow();
            customerlist.ShowDialog();

        }
 private void buttonCustomerManagement_Click(object sender, RoutedEventArgs e)
 {
     CustomerListWindow listWindow = new CustomerListWindow();
     listWindow.ShowDialog(); //difference between show and showdialog -- show allows you to make as many windows as you want whereas showdialog just opens it once
 }