By Brad Brooks and Gabriella Borter UVALDE, Texas (Reuters) -The gunman who killed 19 children and two teachers crossed the grounds of the Texas elementary school without being confronted and entered the building through an unlocked door, authorities said on Thursday, offering another new account of the events that proceeded the massacre. Salvador Ramos, 18, was barricaded inside a classroom at Robb Elementary School for an hour before a tactical team finally breached the room and fatally shot him, police confirmed. Parents outside implored officers to storm the building. The Uvalde school dis…