Noel Paul Stookey has enjoyed an extraordinary career that began as the “Paul” of the seminal 1960s folk trio Peter, Paul & Mary. Their signature vocal harmonies and songs like “Blowin’ In the Wind,” “If I Had a Hammer” and “Puff the Magic Dragon” were the soundtrack of a generation. In March, he released his last EP, “Just Causes,” a carefully curated compilation of 15 Stookey tracks, each bearing a theme of social concern, from hunger to nuclear proliferation, drug trafficking and the environment.