Add "unfollow" feature, allowing users to turn off notifications for replies to their comments/topics

This would allow users to more effectively disengage from arguments. It should probably be something disabled by default and only enabled on a case-by-case basis, not a global user setting though, IMO.

edit: Feature also requested again, but for a slightly different reason (avoiding getting spammed on busy topics) -
https://tildes.net/~tildes/dz7/suggestion_turn_off_reply_notifications_for_a_topic_or_comment_you_made