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/group/everyone/chrisitna/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.
Nit: When we put parameters on a new line, there should be an extra level of indentation to visually separate the parameter list from the body of the function (see [here](http://legacy.python.org/dev/peps/pep-0008/#indentation)). This is also how pycharm and emacs do things by default.

I also think the style we've been using has been to put each parameter on their own line (I'm actually personally fine with the style you used here, but we should make sure we're consistent).