World records

[Qaomen]

Description
We're currently keeping track of users' personal bests and displaying improvements at the end of races, while the feature for world records is currently only partially implemented. It would be nice to keep proper track of world records and display the current WR and any improvements the same way.

Minimum Acceptance Criteria

• The database should keep track of the world record time and the user (id) who set it.
• The server should notify clients of world record improvements on the results score board.
• The client should display the current world record time and holder on the results score board.
• Banned users should not be listed as world record holders. (Similarly, unbanning them should re-check it against their pbs, or clear their personal bests instead?)

Is blocked by the following issues
Affected by #87 and #281