FORT BELVOIR, Va. A new exhibit at the National Museum of the United States Army may be the most extensive collection of Revolutionary War artifacts under one roof since the 1770s."Call to Arms: The Soldier and the Revolutionary War" invites visitors to explore rare relics that witnessed iconic chapters in American history, from Lexington and Concord to the Battle of Bunker Hill.Museum Director Paul Morando said the exhibit was four years in the…