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/ImportBundle/Controller/WallabagV1ControllerTest.php

@@ -127,7 +127,7 @@ class WallabagV1ControllerTest extends WallabagCoreTestCase
         $tags = $content->getTags();
         $this->assertContains('foot', $tags, 'It includes the "foot" tag');
         $this->assertContains('framabag', $tags, 'It includes the "framabag" tag');
-        $this->assertSame(2, \count($tags));
+        $this->assertCount(2, $tags);
 
         $this->assertInstanceOf(\DateTime::class, $content->getCreatedAt());
     }