Arson destroyed an antebellum plantation house that served as the governor’s mansion for nine months during the Civil War and damaged a museum less than a mile away on Thursday, the Louisiana State Fire Marshal's Office said. The Old Governor’s Mansion burned to the ground, but the fire at the Louisiana Orphan Train Museum apparently burned out fairly quickly, said Brant Thompson, chief deputy for the fire marshal’s office. Museum workers found fire damage when they arrived for work Thursday morning, he said. …