Add java8 Optional's support to AccessControlManager

Created by: ssokolenko

This change will allow to pass Optional's to authz checks, e.g.:

AccessControlManager acm = ...
Optional<Party> maybeParty = playAuthApi.getCurrentParty();
Optional<?> maybeResource = repository.findOne(id);

acm.isPermitted(maybeParty, READ, maybeResource);
// or
playAuthApi.isPermitted(READ, maybeResource);