* Wrong exception class: ActiveRecord::RecordNotUnique, not PG::UniqueViolation
It's completely not obvious but PG::UniqueViolation is just a string inside the exception message, not the actual class of the exception
* Favourite does not have target_account_id
* Improve account index migration
- Display more progress in stdout
- Catch PG::UniqueViolation when re-attributing favourites
- Skip callbacks and validations when re-attributing other relationships
* Use in_batches to reduce table lock-up during account merge
* Use #say_with_time to benchmark each deduplication
