Avoid CS search endpoint for non-search queries

This change requires cs_comments_service version 31ef160 or later. Now
that the /threads endpoint can filter by commentable_ids, use that
instead of the /search/threads endpoint, which does not sort and
paginate correctly.

Bug: FOR-224

CHANGELOG.rst

@@ -16,6 +16,12 @@ Blades: Fix bug when the speed can only be changed when the video is playing.
 LMS: Change bulk email implementation to use less memory, and to better handle
 duplicate tasks in celery.
 
+LMS: When a topic is selected in the forums navigation sidebar, fetch
+the thread list using the /threads endpoint of the comments service
+instead of /search/threads, which does not sort and paginate
+correctly. This requires at least version 31ef160 of
+cs_comments_service.
+
 LMS: Improve forum error handling so that errors in the logs are
 clearer and HTTP status codes from the comments service indicating
 client error are correctly passed through to the client.

lms/lib/comment_client/thread.py

@@ -34,7 +34,7 @@ class Thread(models.Model):
                           'recursive': False}
         params = merge_dict(default_params, strip_blank(strip_none(query_params)))
 
-        if query_params.get('text') or query_params.get('tags') or query_params.get('commentable_ids'):
+        if query_params.get('text') or query_params.get('tags'):
             url = cls.url(action='search')
         else:
             url = cls.url(action='get_all', params=extract(params, 'commentable_id'))