Create combined sky map and spacetime coincidence FAR automatically

Similar to waiting for g-events to be complete, we will wait to compare or combine sky maps until the external event is complete:

• comparing: when there is a coincidence (EM_COINC), and both sky maps are available (se: SKYMAP_READY, ext: LUMIN_GO)
• combine: when there is a raven alert (RAVEN_ALERT), and both sky maps are available (se: SKYMAP_READY, ext: LUMIN_GO)

If the external event is not complete we will look whether a superevent sky map is available and apply SKYMAP_READY if it is. Note we also apply SKYMAP_READY to all related external events when the superevent sky map is first available. The first case catches times where the superevent sky map comes in after the coincidence is found (EM_COINC applied) and the latter case catches time where the superevent sky map comes in before the coincidence is found.

gwcelery/tasks/external_skymaps.py

@@ -63,7 +63,6 @@ def get_preferred_skymap(graceid):
     """
     gracedb_log = gracedb.get_log(graceid)
     for message in reversed(gracedb_log):
-        comment = message['comment']
         filename = message['filename']
         if filename.endswith('.fits.gz'):
             return filename