Listen for AuthenticationException

Convert AuthenticationException to AccessDeniedHttpException

Issue #411
Update docs to explain the 401 status code
Add space between elseif and parentheses
Forced @Target("METHOD") to method annotations.
Merge pull request #415 from Dewos/master

Forced @Target("METHOD") to method annotations.
Merge pull request #411 from RLovelett/dev-411

Handle AuthenticationException