Add proper length constraint validations to all string mapped ORM fields, so they show a nice validation error, instead of a 500 error

Fixes issue #544

src/Entity/Parts/MeasurementUnit.php

@@ -50,6 +50,7 @@ use Doctrine\ORM\Mapping as ORM;
 use Symfony\Bridge\Doctrine\Validator\Constraints\UniqueEntity;
 use Symfony\Component\Serializer\Annotation\Groups;
 use Symfony\Component\Validator\Constraints as Assert;
+use Symfony\Component\Validator\Constraints\Length;
 
 /**
  * This unit represents the unit in which the amount of parts in stock are measured.