Pass group_id when getting user thread and comment counts.

TNL-543

Related cs_comments PR is https://github.com/edx/cs_comments_service/pull/122

@jimabramson @dan-f Please review.

Can use my sandbox to test--
http://cahrens.m.sandbox.edx.org/courses/christina/foo/bar/discussion/forum

This course has the following users and posts:
1) staff@example.com has moderator access. staff has started 3 discussions-- one to general (not cohorted), one to Verified Group, one to Honor Group. staff has also commented on two posts-- one written by honor to everyone, and one written by honor just to Honor Group cohort.

2) honor@example.com is in Honor Group. honor has created 2 posts, 1 to everyone and 1 to Honor Group. honor has also commented on both of those posts.

3) verified@example is in Verified Group. verified has created 2 posts, 1 to everyone and 1 to Verified Group.
No, the 2 requests are identical, except that one is for a specific course, and the other is not.

And I do think that course_id and group_id are correlated. Whenever asking for user information for a specific course, the group_id should also be present (if the course is cohorted and the user does not have moderation privileges). 

Here are the requests. Unfortunately I can't think of a way to improve the test.

1) call('get', 'http://localhost:4567/api/v1/users/2', headers={'X-Edx-Api-Key': None, 'Accept-Language': 'en'}, params={'complete': True, 'request_id': UUID('b16c6f21-3c57-46d1-a110-431e4961ea94')}, timeout=5, data=None)

2) call('get', 'http://localhost:4567/api/v1/users/2', headers={'X-Edx-Api-Key': None, 'Accept-Language': 'en'}, params={'course_id': u'org.9/course_9/Run_9', 'group_id': 1, 'complete': True, 'request_id': UUID('f98f9608-3994-4456-99ba-29a3f0e41a08')}, timeout=5, data=None)