Last year it was Dreamgirls. The year before, Hairspray. And now Signature Theatre has staged another holiday season treat, what you might call the mother of them all, Gypsy. All three shows are quintessential American musicals, exploring aspects of mass-produced American culture and entertainment. Gypsy, of course, covers the most ground, from the peak and decline of vaudeville to the rise and enduring popularity of more risqué entertainment forms, such as burlesque. The Arthur Laurents-Jule Styne musical is chiefly inspired by the life of striptease artist Gypsy Rose Lee, with a special focus on her overbearing mother, Mama Rose, who pushed her two daughters June and Louise to be the stars she never was.