improved code styles #158 (#172)

* use php-cs-fixer instead of phpcodesniffer
* updated scrutinizer config
* adjusted code yules to all files
* updated CONTRIBUTING guidelines

src/Controller/ActivityController.php

@@ -10,7 +10,6 @@
 namespace App\Controller;
 
 use Symfony\Bundle\FrameworkBundle\Controller\Controller;
-use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;
 use Sensio\Bundle\FrameworkExtraBundle\Configuration\Security;
 use App\Entity\Activity;
 use App\Repository\ActivityRepository;
@@ -22,7 +21,6 @@ use App\Repository\ActivityRepository;
  */
 class ActivityController extends Controller
 {
-
     /**
      * @return ActivityRepository
      */