This 1978 miniseries is being repeated, quite appropriately, by BET to acknowledge Martin Luther King Day, which is tomorrow. But when this NBC drama first was televised, it was timely, too: Its telecast marked 10th anniversary of the assassination of Martin Luther King, Jr., and it drew a very esteemed roster of talent to the project. Abby Mann, who wrote Judgment at Nuremberg for Playhouse 90, wrote and directed the miniseries. And what a cast: Paul Winfield plays King, Cicely Tyson is his wif