#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/admin.py

@@ -29,6 +29,7 @@ class CompensationAdmin(BaseObjectAdmin):
         "identifier",
         "title",
         "created",
+        "deleted",
     ]