public static ChangePasswordWindow ReturnInstance(MainGUI main, User u)
 {
     if (ChangePasswordWindow.instance == null)
         ChangePasswordWindow.instance = new ChangePasswordWindow(main, u);
     return ChangePasswordWindow.instance;
 }
 private void Window_Closing(object sender, System.ComponentModel.CancelEventArgs e)
 {
     ChangePasswordWindow.instance = null;
 }