Added RbacAwareInterface.php

```
// MyService.php
<?php
namespace MyModule\Service;

use ZfcRbac\Service\RbacAwareInterface;

class MyService implements RbacAwareInterface
{
    public function setRbac($rbac) { ... }
}

// Module.php
<?php
public function getServiceConfig()
{
	return array(
        'initializers' => array(
            'rbacService' => function($service, $serviceManager) {
                if ($service instanceOf RbacAwareInterface) {
                    $service->setRbac($serviceManager->get('service.security'));
                }
            },
        ),
	);
}