NEW YORK (Reuters) - Nancy Shevell, the American heiress married to former Beatle Paul McCartney, on Wednesday resigned from the board of New York's Metropolitan Transportation Authority where she served since 2001. "In my 30-year professional career, this has been a highlight for me," Shevell told the board which oversees the New York area's bridges, tunnels and mass transit systems. "Thank you so much. I am so very emotional and sad right now," she added. She did not give a reason for her decision to step aside. ...