LOS ANGELES/SAN FRANCISCO (Reuters) - Clamshell grills are making burger flipping obsolete at McDonald’s, Johnny Rockets and other burger chains. Digital kiosks, tabletop tablets and mobile phones are taking orders at eateries like Panera, Chili’s Grill & Bar and Domino’s. And at Silicon Valley start-up Zume, robots are being programmed to take over pizza assembly.