HBO Films has teamed with writer Kirk Ellis, producer Doug Ellin and Steven Spielberg’s Amblin TV for a project about Harriet Tubman, with Oscar nominee Viola Davis set to portray the famous abolitionist. Based on the biography Bound For The Promised Land by historian Kate Clifford Larson, the film, now in development, tells the story of American hero Tubman. Born a slave, she escaped and, via an intricate escape network of secret routes and safe houses known as the…