#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

konova/models/object.py

@@ -10,6 +10,7 @@ import uuid
 from abc import abstractmethod
 
 from django.contrib import messages
+from django.db.models import QuerySet
 
 from konova.tasks import celery_send_mail_shared_access_removed, celery_send_mail_shared_access_given, \
     celery_send_mail_shared_data_recorded, celery_send_mail_shared_data_unrecorded, \
@@ -124,7 +125,7 @@ class BaseObject(BaseResource):
             self.log.add(action)
 
             # Send mail
-            shared_users = self.users.all().values_list("id", flat=True)
+            shared_users = self.shared_users.values_list("id", flat=True)
             for user_id in shared_users:
                 celery_send_mail_shared_data_deleted.delay(self.identifier, user_id)
 
@@ -464,6 +465,15 @@ class ShareableObjectMixin(models.Model):
         # Set new shared users
         self.share_with_list(users)
 
+    @property
+    def shared_users(self) -> QuerySet:
+        """ Shortcut for fetching the users which have shared access on this object
+
+        Returns:
+            users (QuerySet)
+        """
+        return self.users.all()
+
 
 class GeoReferencedMixin(models.Model):
     geometry = models.ForeignKey("konova.Geometry", null=True, blank=True, on_delete=models.SET_NULL)