The recovery mechanism when a flake is scaled down.
1. Restores the state associated with all the keys from the neighbor flake from backup into the main state.
2. Replays the messages backed up for that flake, if required.
3. Updates the token ring.
  3a. Mappers update their ring to change the owner.
  3b. reducers update their ring to reflect the new neighbors (currently, a possible bug here.)

Fixes #39