(Reuters) - European shares advanced on Thursday as investors awaited the outcome of a general election in Britain that may decide the future of Brexit as well as comments from new European Central Bank (ECB) chief Christine Lagarde.The FTSE 100 index comprising internationally-focused firms gained 0.6%, shrugging off the impact from a firmer sterling. The pan-European STOXX 600 index rose 0.3%.While all major opinion polls suggested that the ruling Conservative Party will win Thursday's..