LAS VEGAS (AP) — A massive winter storm set the stage for a brutal travel day Sunday, with airlines warning of widespread cancellations and delays at some of the nation’s busiest airports. Widespread snow, sleet and freezing rain threatened nearly 180 million people — more than half the U.S. population — in a path stretching from the southern Rocky Mountains to New England, the National Weather Service said Saturday night. After sweeping through the South, forecasters said the storm was