Matthew Schaefer’s focus wasn’t on becoming a marketer’s dream. The Islanders’ prized rookie longed only to be a superior NHL player as quickly as possible. But the combination of the No. 1 overall pick’s confident yet humble demeanor — along with his superb play — makes him not only a natural to be the face of the Islanders but a young, marketable star with broader appeal for the NHL. In the competitive New York market, Schaefer could eventually elevate the Islanders’ brand to equal footing wit