CONN-401 consistent thread count filtering

The sub-forum thread filtering excludes `comments_index` rows where `archived != 0`. This results in inconsistent numbering between the per forum thread counts in [`getBoardInfo` (https://github.com/Wikia/app/blob/dev/extensions/wikia/Forum/ForumBoard.class.php#L36) and the total thread count displayed at the top of the page.

/cc @owend