Enable PHPStan

- Fix error for level 0 & 1 (level 7 has 699 errors...)
- Add `updated_at` to site_credential (so the `timestamps()` method applies correctly)

tests/Wallabag/CoreBundle/Controller/ConfigControllerTest.php

@@ -1,6 +1,6 @@
 <?php
 
-namespace tests\Wallabag\CoreBundle\Controller;
+namespace Tests\Wallabag\CoreBundle\Controller;
 
 use Tests\Wallabag\CoreBundle\WallabagCoreTestCase;
 use Wallabag\AnnotationBundle\Entity\Annotation;