Guard support

[UFOMelkor]

The service-bus has two plugins to support authorization, the RouteGuard and the FinalizeGuard.
Both rely on a simple interface AuthorizationService.

Any thoughts about …

• … adding a AuthorizationService adapter for Symfony\Component\Security\Core\Authorization\AuthorizationCheckerInterface
• … allowing to enable each guard for each message-bus per configuration
• … adding an (optional) event listener to convert Prooph\ServiceBus\Plugin\Guard\UnauthorizedException into Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException if it is not caught in the controller.

[prolic]

@UFOMelkor

• Adding an implementation of AuthorizationService in the bundle is a good idea, but I would do it for 1.1 release, not targeting upcoming 1.0 release, as this would only delay the final release (and it's not a strict requirement).

• about enabling guards per bus: the guards are plugins, so it should already be possible to add them simply

• convert Prooph\ServiceBus\Plugin\Guard\UnauthorizedException into Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException - same as above, I would target this for 1.1 release.