POP star Herman of Herman and the Hermits managed to raise a cheerful smile yesterday as he wrote out a cheque.     But he wasn't feeling very cheerful and neither was songwriter Graham Gouldman, 19, whose shoulders Herman used as a desk.     For Customs officers at Manchester Airport seized a gold disc awarded to the group in America.     And they imposed duty of more than £300 on gifts the group brought home at the end of a world tour.     Which was why Herman, 18, had to write out the cheque.