#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/managers.py

@@ -35,9 +35,7 @@ class CompensationManager(models.Manager):
 
     """
     def get_queryset(self):
-        return super().get_queryset().filter(
-            deleted__isnull=True,
-        ).select_related(
+        return super().get_queryset().select_related(
             "modified",
             "intervention",
             "intervention__recorded",