API: changed date-format, camelCase instead of snake_case, null values, update and create for customer and project (#718)

src/API/BaseApiController.php

@@ -12,7 +12,10 @@ declare(strict_types=1);
 namespace App\API;
 
 use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
+use Symfony\Component\Form\Extension\Core\Type\DateTimeType;
 
 abstract class BaseApiController extends AbstractController
 {
+    public const DATE_FORMAT = DateTimeType::HTML5_FORMAT;
+    public const DATE_FORMAT_PHP = 'Y-m-d\TH:m:s';
 }