Superevents

Adding superevents to GraceDB, including the necessary models, utility functions, and API resources. This has also resulted in changes to the overall configuration and some parts of the events model.

Many models in the events app, like Labels, Tags, EventLogs, etc. were needed in a similar form for superevents. We were able to completely reuse the existing Label and Tag models for superevents. In other cases, we had to abstract the main functionality of the class into an abstract base class and then implement separate models for events and superevents, due to foreign key requirements. This should leave the current functionality of the events models unchanged.

Some portions of the events API have been modified because of one of the following reasons:

• It didn't make sense and was unnecessarily difficult to duplicate for superevents
• It was inefficient or bad

These changes are documented here: https://bugs.ligo.org/redmine/issues/6133

gracedb/superevents/models.py

@@ -60,13 +60,7 @@ class Superevent(CleanSaveModel, ModelToDictMixin):
     # Class method overrides --------------------------------------------------
     def clean(self, *args, **kwargs):
 
-        # If preferred event is not set, just pick the first non-external
-        # event in the set
-        # NOTE: do we actually want to do this?
-        if self.events.exists() and not self.preferred_event:
-            self.preferred_event = self.events.exclude(group__name=
-                settings.EXTERNAL_ANALYSIS_GROUP).first()
-
+        # External events can't be set as preferred events
         if (self.preferred_event and self.preferred_event.group.name ==
             settings.EXTERNAL_ANALYSIS_GROUP):
             raise ValidationError({'preferred_event':