reset password strategy, so it can live in app/lib
remove unused file
we dont need it
update password strategy to make it directly response json data
add error baner to login form
try fix bug 'ArgumentError (A copy of PasswordStrategy has been removed from the module tree but is still active)' ,but not succeed. It looks more like a limitation but not a bug in ActiveSupport. See also https://github.com/37signals/mail_view/issues/37.