Proposal - allow to omit 'roles' in annotation

This change allows very simple migration from JMS to your bundle - only need to replace
```
-use JMS\SecurityExtraBundle\Annotation\Secure;
+use Lsw\SecureControllerBundle\Annotation\Secure;
```

and don't need to replace 
```
-     * @Secure("ROLE_VIEW")
+     * @Secure(roles="ROLE_VIEW")
```

in each action method