Filter out replies when calculating issue counts.
Issue counts on review requests were going up when replies were made to

comments with issues. This happened because we looked for all comments,

and not just top-level comments, when calculating issue counts and when

deciding whether to increase issue counts.
We now limit these only to top-level reviews/comments.
I also noticed that we were bumping the last review activity timestamp

even when a review was still in draft mode. That's been fixed so that

the value is only updated when the review is public.

Unit tests pass.
Replied to a comment, and didn't see the count go up.