accounts: added lock method
accounts: added lock method

gsalgado/pyethapp,ethereum/pyethapp,RomanZacharia/pyethapp,changwu-tw/pyethapp,gsalgado/pyethapp,RomanZacharia/pyethapp,changwu-tw/pyethapp,kustomzone/pyethapp,vaporry/pyethapp,d-das/pyethapp,ethereum/pyethapp