[admin] new snapshot versioning convention
- version to 0.0-snap
- mainline snapshot version will be <maj>.<min>-snap from
  now on. This is an invalid npm version so it should never
  be used for publishing. Linking should be OK, though.
[#63129458] completed
- all http statuses reference
- convert 400-599 into error constructors
- port handler from leaderboard
- attach errors to rest util exports