By Renee Maltezou and George Georgiopoulos ATHENS (Reuters) - Germany's finance minister told Greeks to stop lobbying for more debt forgiveness during a visit to Athens on Thursday that forced authorities to shut the city center and ban protests against the deeply unpopular champion of austerity. Visiting the country for the first time since its debt problems kindled the euro zone crisis four years ago, Wolfgang Schaeuble's motorcade drove through streets empty except for riot police to meet a packed audience of Greek businessmen. ...