#31 API POST Compensation

* adds support for POST of new compensations
* adds shared_users property to BaseObject and Compensation to simplify fetching of shared users (Compensation inherits from intervention)
* extends compensation admin index
* modifies compensation manager which led to invisibility of deleted entries in the admin backend
* fixes bug in sanitize_db.py where CREATED useractions would be removed if they are not found on any log but still are used on the .created attribute of the objects

compensation/models/compensation.py

@@ -245,6 +245,15 @@ class Compensation(AbstractCompensation, CEFMixin, CoherenceMixin):
         # Compensations inherit their shared state from the interventions
         return self.intervention.is_shared_with(user)
 
+    @property
+    def shared_users(self) -> QuerySet:
+        """ Shortcut for fetching the users which have shared access on this object
+
+        Returns:
+            users (QuerySet)
+        """
+        return self.intervention.users.all()
+
     def get_LANIS_link(self) -> str:
         """ Generates a link for LANIS depending on the geometry