Leaderboard score offsets under the governor's control

[jaybuidl]

Rationale

The leaderboard scores may need adjustments via governance in some cases

1. When a dispute cannot be resolved due to technical issues, then the jurors should be penalized.
2. When migrating to a new deployment, the offsets allow carrying over the scores between deployments.

Solution

Rely on a contract to emit score offset events per juror. The events should be picked up by the subgraph to apply the offsets to the scores.