api: Set include_deactivated_groups client capability

We currently don't look at the list of groups at all.
When we start doing so, we'll be sure to properly handle
the possibility that some of the groups are deactivated.

Author: gnprice

lib/api/route/events.dart

@@ -18,6 +18,7 @@ Future<InitialSnapshot> registerQueue(ApiConnection connection) {
       'user_avatar_url_field_optional': false, // TODO(#254): turn on
       'stream_typing_notifications': true,
       'user_settings_object': true,
+      'include_deactivated_groups': true,
       'empty_topic_name': true,
     },
   });