Over his long career Barry Manilow has earned fifty Top-40 hits, along with a Grammy, a Tony and two Emmys. Today, at 80, he is about to debut his Broadway musical, “Harmony,” the true story of a pre-World War II singing group in Germany whose fame was obliterated by the Nazis. Correspondent David Pogue talks with Manilow about his pop career, and his long interest in musical theater.