Fix comment styling

Commit 59426e72cb broke the styling for threaded comments by ommiting
`|fill_tree|annotate_tree` template tag filters on the comment list.

These filters add the parent_id, open, and close attributes to comments,
and are essential for rendering comments.

Fixes #1549, #1550, and #1551
Merge pull request #1552 from maurizi/fix-comment-styling

Fix comment styling