[WIP] adding worker aggregate listeners (2)

retake on https://github.com/juriansluiman/SlmQueue/pull/76
The [usual pattern for ZF2](https://github.com/zendframework/zf2/blob/master/library/Zend/Mvc/Application.php#L296) (which I like more) is:

```php
$result = $eventManager->trigger(WorkerEvent::EVENT_PROCESS_QUEUE_PRE, $workerEvent);

if ($result->stopped()) {
    //
}
```