* Ensure EvoDB consistency by storing the best block hash
This approach is similar to the one used for chainstate currently.
Ensures that:
- nodes that upgraded after DIP3 has all the data processed correctly (they will crash and require reindex);
- evodb/ is removed when blocks/ is removed (otherwise sync will fail due to duplicate records).
* Implement CEvoDB::VerifyBestBlock/WriteBestBlock and call them from ConnectBlock/DisconnectBlock
* Fix walletbackup.py
