Musicals of the 1970s were a combustible combination of Liza Minnelli, John Travolta, “The Rocky Horror Picture Show,” The Ramones and disco music. The happy endings and light hearted dance numbers that highlighted glamorous gams was becoming a thing of the past, unless those gams belonged to a transvestite from another galaxy. Musicals also tackled a variety of unusual subjects such as the rise of Nazism in “Cabaret,” and the Russian revolution in “Fiddler on the Roof.”