misc fixes for Thirdparty / addPerson

* set default values for ThirdParty in ThirdParty.vue
* set correct value for binding with phone (telephone instead of
phonenumber)
* add validation on ThirdParty/denomination: at least two characters, no
Null value

src/Bundle/ChillMainBundle/Entity/Address.php

@@ -139,12 +139,10 @@ class Address
     private $point;
 
     /**
-     * @var PostalCode
-     *
      * @ORM\ManyToOne(targetEntity="Chill\MainBundle\Entity\PostalCode")
      * @Groups({"write"})
      */
-    private $postcode;
+    private ?PostalCode $postcode;
 
     /**
      * @var string|null