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/EventSubscriber/NavbarShowUserSubscriber.php

@@ -50,7 +50,7 @@ class NavbarShowUserSubscriber implements EventSubscriberInterface
      */
     public function onShowUser(ShowUserEvent $event)
     {
-        if ($this->storage->getToken() === null) {
+        if (null === $this->storage->getToken()) {
             return;
         }