wip: Per-domain policy support

* The domain edition form was converted to a "TabsForm"
* New events added : "ExtraDomainForm" and "FillDomainInstances"
* Creation and modification of policies work

see #260

lib/events.py

@@ -42,6 +42,9 @@ events = [
     "ExtraAccountForm",
     "CheckExtraAccountForm",
     "FillAccountInstances",
+
+    "ExtraDomainForm",
+    "FillDomainInstances",
     
     "GetExtraRoles",
     

lib/tables.py

@@ -28,14 +28,10 @@ class Column:
     def __unicode__(self):
         try:
             label = getattr(self, "label")
-        except KeyError:
+        except AttributeError:
             label = getattr(self, "name")
         return _(label)
 
-    def __str__(self):
-        return self.__unicode__()
-
-
 class SelectionColumn(Column):
     """Specific column: selection