Before the rock music of “Hair” and “Jesus Christ Superstar,” before the ironies of Stephen Sondheim, before the bleak visions of Kander and Ebb, before the epic stagings of “Phantom” and “Les Miz,” Broadway musicals relied on at least one of three elements: hummable melodies that could be recorded by pop singers, roles where a star could bewitch the audience and a conflict-and-resolution structure dating to operettas of the 19th century.Read MORE