- Pending validator updates do not prevent elections from concluding.
- ValidatorElection overrides has_conclude to not conclude when there is a pending update for the matching height.
- Effective validator updates deem past elections inconclusive.
- Do not conclude migration election if there is a migration in progress.
- Rewrite election tests to not use mocks and assert many different things.
- Record concluded elections in the `election` collection.
* Problem: We need a way to synchronize a halt to block production to allow for upgrades across breaking changes.
* Solution: Created `MigrationElection`.
* Problem: Need documentation for `migration` elections.
* Solution: Updated the docs.
* Problem: `MigrationElection` needs 'new' CLI method.
* Solution: Updated the definition of `election` to include the new `migration` type.
* Problem: The way `end_block` checks for concluded elections assumes there is only one type of election (so we can't conclude an `upsert-validator` and a `chain-migration` at the same height).
* Solution: Re-engineered the code in `Elections` to conclude multiple elections in the same block. If more than one election change the validator set, only one of them is applied.
* Problem: Tendermint change to store validator changes at height h+2 will break `Election.get_status`.
* Solution: Reworked `get_validator_change` to look at only the latest block height or less.
