Suggestion: New Event after eMail was sent (#151)

* - Added new event to make message object available for editing (e.g. attaching signers) before sending

* shorter event name
included $params and $form

* Adding new Event after eMail was sent

* changed event name for consistency

email.php

@@ -165,6 +165,9 @@ protected function sendFormEmail($form, $params, $vars)
 
         // Send e-mail
         $this->email->send($message);
+
+        //fire event after eMail was sent
+        $this->grav->fireEvent('onEmailSent', new Event(['message' => $message, 'params' => $params, 'form' => $form]));
     }
 
     protected function isAssocArray(array $arr)