O4a online dtdphi plotter

This patch allows the following dtdphi plot to be uploaded to gracedb page.
Example G-event pages:
MDC 3-ifo event (two dtdphi plots)
MDC 2-ifo event (one dtdphi plot)
MDC 1-ifo event (no dtdphi plot)

TODO:

• test with single triggers
• test with online small analysis
• try adding LV plot and see if that is informative any way

gstlal-inspiral/bin/gstlal_ll_inspiral_event_plotter

@@ -507,9 +507,11 @@ class EventPlotter(events.EventProcessor):
 	def upload_dtdphi_plots(self, event):
 		sngl_inspiral_table = lsctables.SnglInspiralTable.get_table(event['coinc'])
 		offset_vectors = lsctables.TimeSlideTable.get_table(event['coinc']).as_dict()
+		assert len(offset_vectors.keys()) > 1, "the time slide table has multiple time-slide entries"
+		offset_vector = offset_vectors[list(offset_vectors.keys())[0]]
 		rankingstat, _ = far.parse_likelihood_control_doc(ligolw_utils.load_filename(event['ranking_data_path'], contenthandler = far.RankingStat.LIGOLWContentHandler))
 
-		event_kwargs = rankingstat.kwargs_from_triggers(sngl_inspiral_table, offset_vectors)
+		event_kwargs = rankingstat.kwargs_from_triggers(sngl_inspiral_table, offset_vector)
 		ifos = sorted(event_kwargs["snrs"].keys())
 		ifo1 = ifos.pop(0)
 		snrs = event_kwargs["snrs"]