Tweak counts of the nits and comments to better focus reviewer attention

This suggests changes to the counts displayed on the dashboard. Here:

- Nits are counted only if they are submitted by others, so a user can
  comment on their own code without "penalty".

- The arguments/discussions count only goes up when the user
  participates in the discussion. This is a different kind of signal
  than a third user chiming in, as it shows that the user has
  (implicitly) acknowledged the feedback of the nit.

- A new number is shown reflecting the revision count of the submission.
  This helps a potential nitpicker better distinguish early code from
  code that is likely closer to the end.

Basic tests are added for each kind of data. The routines that sort
pending requests have also been adjusted to conform to this suggestion.

I also suggest a change to how discussion threads are described on the 
dashboard, changing "arguments" to something more descriptive.