models: OrganizationalUnit should just inherit from base Model for cl…

…arity

Having it inherit of Samba's OrganizationalUnit model just makes it unclear.

And it makes it easier to donate upstream again later.

src/sambal/models/org.py

@@ -1,12 +1,20 @@
-from samba.domain import models
-from samba.domain.models.fields import IntegerField
+from samba.domain.models.fields import IntegerField, StringField
+from samba.domain.models import Model
 
 
-class OrganizationalUnit(models.OrganizationalUnit):
-    """OrganizationalUnit contains additional fields not in Samba yet.
+class OrganizationalUnit(Model):
+    """OrganizationalUnit container model.
 
-    This is an example where the original Samba model can be overridden.
-    The resource must be set up to use this model over the Samba one.
+    This model exists in upstream Samba but many of the fields are missing.
+    The model is declared again here which overrides the original.
     """
 
+    ou = StringField("ou")
     country_code = IntegerField("countryCode")
+
+    def __str__(self):
+        return str(self.ou)
+
+    @staticmethod
+    def get_object_class():
+        return "organizationalUnit"