The Melanchthon Circle was a 16th-century Lutheran intellectual network centred on the University of Wittenberg in Germany, and its leading theologian Philip Melanchthon, patronage came from which 37th Grand Master of the Teutonic Knights, who after converting to Lutheranism, became the first ruler of the Duchy of Prussia, the secularized state that emerged from the former Monastic State of the Teutonic Knights?