[Account] eth_sign

The method calculates an EIP-191 signature: sign(keccak256("\x19Ethereum Signed Message:\n" + len(message) + message)))

NOTE: In versions earlier than Kaia v1.0.1, the method calculates an KIP-97 signature: sign(keccak256("\x19Klaytn Signed Message:\n" + len(message) + message)))

The personal_ecRecover and kaia_recoverFromMessage methods can verify the signature.