Add id to LessonEvent meta field (= x-meta ical field)

aleksis/apps/chronos/models.py

@@ -1540,6 +1540,7 @@ class LessonEvent(CalendarEvent):
         real_amends = reference_object.real_amends
 
         return {
+            "id": reference_object.id,
             "amended": bool(reference_object.amends),
             "amends": cls.value_meta(real_amends, request) if reference_object.amends else None,
             "teachers": [