Created|Deleted refactoring

* refactors base attributes created and deleted into UserActionLogEntry foreign keys
* refactors all related queries and process logic
* fixes binding_on into binding_date in intervention/detail/view.html
* adds basic __str__ for some models
*

compensation/tables.py

@@ -51,7 +51,7 @@ class CompensationTable(BaseTable):
     lm = tables.Column(
         verbose_name=_("Last edit"),
         orderable=True,
-        accessor="created_on",
+        accessor="created__timestamp",
     )
 
     class Meta(BaseTable.Meta):
@@ -173,7 +173,7 @@ class EcoAccountTable(BaseTable):
     d = tables.Column(
         verbose_name=_("Created on"),
         orderable=True,
-        accessor="created_on",
+        accessor="created__timestamp",
     )
     ac = tables.Column(
         verbose_name=_("Actions"),