It has been more than 50 years since the motion picture “Guess Who’s Coming to Dinner” was released.It’s about a liberal newspaper editor and publisher, Matt Drayton, played by Spencer Tracy in his very last role, with Katherine Hepburn as his progressive wife, Christina, asked to give their blessing to the marriage of their daughter Joanna to a handsome, black doctor, John Prentice, played by Sidney Poitier.A lot has happened since 1967. Martin Luther King Jr. was assassinated on April 4, 1968, and …