#36 Bring back time-warped standings

[Bruce Merry]

In the change to make standings per-group instead of per-server, I ripped out some of the code that meant that a submission made at contest time X would only become visible (in standings) to another contestant when their contest time was >= X, even if that meant holding back information until later.

Supporting this will require each server to maintain a separate standings table for each user. The performance impact will need to be checked as standings updates are one of the slower parts of abacus.

[Bruce Merry]

If this is tackled, bugs 33 and 34 should be re-tested as they were never fundamentally fixed, just closed because they no longer manifest without the time-warped standings.