The Prom, now playing at the Longacre Theatre, might just be the show that single-handedly puts the Broadway back into Broadway musicals. With rare yet notable exceptions, most of them Tony winners -- Fun Home, Hamilton, Come From Away, The Band’s Visit and Dear Evan Hansen (the latter of which The Prom is a close cousin of but the cheerier, more bubbly sort) -- most musicals being produced today are based on branded properties: film or book adaptations, jukebox creations where the songs are guaranteed to be memorable hits (they already are) or pop culture icons (Spiderman: Turn Off The