WIP: Add RAVEN VOEvent variant

• Add new fields to the VOEvent model here
• Add processing of these fields to the superevents API here, including validation
• Add processing and validation of these fields to the events API here
• Add new fields to the VOEvent files here
• Determine which external event needs to be included in the VOEvent
• Load in external event

gracedb/annotations/voevent_utils.py

@@ -60,6 +60,7 @@ def construct_voevent_file(obj, voevent, request=None):
         obj_is_superevent = True
         event = obj.preferred_event
         graceid = obj.default_superevent_id
+        # ext_event = obj.em_events ???
         obj_view_name = "superevents:view"
         fits_view_name = "api:default:superevents:superevent-file-detail"
     else:

[Brandon Piotrzkowski]

I'm running into the issue that you brought up earlier @tanner.prestegard and that I was worried about: how exactly do we choose which external event to grab? Well we want the first one, that with the superevent, is publishable but there's no obvious way to know which at this step. I see a few possible solutions:

1. Pass the external event ID as an argument when calling the VOEvent to be created in gwcelery
2. Create a field within a superevent that determines which external event (or events) pass coincidence threshold that is updated in gwcelery
3. Calculate which events pass coincidence threshold in gwcelery (bad because this would introduce a circular dependency on gwcelery.)

[Brandon Piotrzkowski]

Follow-up to this: how do we get the external event here? It seems we need to give the superevent a property (say event.ext_event) with the external event dictionary prior to this, which I don't know exactly where or how to do this best.