(Reuters) - Shopping centre operator Hammerson Plc on Wednesday appointed AIG executive James Lenton as its new finance chief, months after saying Timon Drakesmith would step down from the role this year.Lenton, whose LinkedIn page says he was chief financial officer of the U.S. insurer's EMEA business and its European Group until June, will take over the role from Oct. 1.Hammerson and its peers are struggling with a tough retail environment in Britain, which has seen several high-profile..