Feature/Eventmanager

here is a simple EventManager to customize the SeoStats logic for the own business.

please give me some feedback to this idea, currently this is not tested.

```php
// usage add listener
$em = \SEOstats\Helper\EventManager::getInstance();
$em->add('google::gCurl::pre_exec',function($event) {
  // some magic
});
$em->add('google::gCurl::post_exec',function($event) {
  // some magic
});
```


```php

// logic in Services
$em = \SEOstats\Helper\EventManager::getInstance();

$e = new \SEOstats\Helper\Event();
$e->setProp('curlHandle', $ch);

$em->trigger(__METHODE__ . '::pre_exec', $e);
```