feat(ui): deduplicate silences

If all alerts in a group are silenced and the same silence ID is used for all of them then there's no point in rendering silence object for each of the alerts, since they are all identical. Move the silence rendering to the footer if that happens so we save screen space

ui/src/Models/API.js

@@ -44,7 +44,8 @@ const APIGroup = PropTypes.exact({
   }),
   shared: PropTypes.exact({
     annotations: PropTypes.arrayOf(Annotation).isRequired,
-    labels: PropTypes.object.isRequired
+    labels: PropTypes.object.isRequired,
+    silences: PropTypes.object.isRequired
   }).isRequired
 });