This changes the "activity" topic-sorting method to look for
"interesting" activity instead of everything, and adds a new "All
activity" method that retains the previous behavior.
Currently, "interesting activity" excludes any comments that have active
Noise, Offtopic, or Malice labels, or any of their children. These
checks are also done based on labeling activity, so for example if
someone posts a new comment it will bump the thread initially, but if
that comment is then labeled as Noise, the thread will "un-bump" and go
back to its previous position in the Activity sort.
There were also some other minor changes made to appearance to support
adding another sorting option, such as shortening the displayed names on
the "tabs", like showing "Votes" instead of "Most votes". This probably
needs some further work, but is okay for now.