* Problem: `ValidatorElection` and `MigrationElection` need to inherit from a common `Election` class.
Solution: Factored the common logic out of `ValidatorElection` and moved it to `Election` parent class.
* Problem: No need to store different types of elections in their own tables
Solution: Remove `DB_TABLE` property from `Election` class.
Solution: Created the `elections` table with secondary_index `election_id`.
* Problem: `UpsertValidatorVote` can be generalized to just be `Vote`
Solution: Renamed, refactored and moved the `Vote` class to tie in with the more general `Election` base class.
* Problem: `election_id` is not unique if two elections have the same properties.
Solution: Added a random `uuid4` seed to enforce uniqueness.
David Dashyan
Lev Berman
Zachary Bowen