By Jeff Mason and Steve Holland WASHINGTON (Reuters) - President Barack Obama outlined plans on Thursday to limit the use of U.S. drone strikes against extremists abroad and took steps aimed at breaking a deadlock on closing the Guantanamo Bay military prison. In a major foreign policy speech after two weeks of fending off domestic scandals, Obama limited the scope of what his predecessor, George W. Bush, had called a global war on terror after the September 11, 2001, attacks. "Our nation is still threatened by terrorists," Obama said at Washington's National Defense University. ...