Account recovery in restored wallet

If a user backs up a wallet, then creates new accounts, then later loses the wallet and restores from backup, the accounts created afterwords can probably be recovered by generating new private keys (as our key generation is deterministic) and looking them up on the blockchain.

This is now implemented via the wallet_recover_accounts API call. This call takes two arguments; the first is the number of accounts to attempt to recover, and the second is the maximum number of keys to generate while trying to recover accounts. After recovering accounts, the blockchain is rescanned and the number of successful recoveries is printed.