Add support for Swift GRB FAR

In support of: https://git.ligo.org/lscsoft/gracedb/merge_requests/32

Ingests a 'FAR' field in Hz and adds it to the event data model. If
the field is present, then show it in the GRB event table on the
detail page.

gracedb/events/translator.py

@@ -646,5 +646,12 @@ def populateGrbEventFromVOEventFile(filename, event):
             break
     event.trigger_id = trigger_id
 
+    # Check for the existance of FAR in the VOEvent_params. if it exists,
+    # Then add it to the event. This change was made on 2/7/2020 in support
+    # of SWIFT event uploads. Note: FAR is in Hz.
+
+    if ('FAR' in VOEvent_params):
+        event.far = float(VOEvent_params.get('FAR').get('value'))
+
     # Save event
     event.save()

gracedb/templates/gracedb/event_detail_GRB.html

@@ -74,6 +74,9 @@
         {% if object.trigger_duration %}
 		<tr><th>Trigger duration</th><td colspan="2">{{object.trigger_duration}}</td></tr>
         {% endif %}
+        {% if object.far %}
+		<tr><th>FAR (Hz)</th><td colspan="2">{{object.far}}</td></tr>
+        {% endif %}
         {% if object.t90 %}
 		<tr><th>T90</th><td colspan="2">{{object.t90}}</td></tr>
         {% endif %}