ATHENS (Reuters) - President Barack Obama said on Tuesday the U.S. stood 'shoulder to shoulder' with Greece, acknowledging the crisis-hit country had made progress on economic adjustment, but had challenges ahead. "Greece has gone through very challenging and dramatic times over the last several years. It has been the policy of my administration to do everything we can to work with the Greek government and the Greek people to restore growth, optimism, to alleviate hardship," Obama told Greek President Prokopis Pavlopoulos in Athens. Obama arrived in the Greek capital earlier Tuesday. ...