By Jamie Freed, Rajesh Kumar Singh and David Shepardson WASHINGTON (Reuters) -U.S. flights were slowly beginning to resume departures and a ground stop was lifted after the Federal Aviation Administration (FAA) scrambled to fix a system outage overnight that had forced a halt to all U.S. departing flights. The cause of the problem, which delayed thousands of flights in the United States, was unclear, but U.S. officials said they had so far found no evidence of a cyberattack. “Normal air traffic operations are resuming gradually across the U.S. following an overnight outage to the Notice to Air…