api: Message signing RPCs are EIP-191 compliant

[blukat29]

Proposed changes

• There were two different message signing standards in Klaytn
  • EIP-191. Prepend "\x19Ethereum Signed Message:\n" + len(message) to the message before signing
  • KIP-97. Prepend "\x19Klaytn Signed Message:\n" + len(message) to the message before signing
• In this PR,
  • Message signing RPCs (i.e. signature producers) are now EIP-191 compliant
  • Message verifying RPCs (i.e. signature consumers) accept both EIP and KIP if possible, only EIP otherwise.

RPC	Implementation	Before PR	After PR
personal_sign	PrivateAccountAPI.Sign	KIP-97	EIP-191
eth_sign	EthereumAPI.Sign	KIP-97	EIP-191
kaia_sign	PublicTransactionPoolAPI.Sign	KIP-97	EIP-191
personal_ecRecover	PrivateAccountAPI.EcRecover	KIP-97	EIP-191
kaia_recoverFromMessage	PublicTransactionPoolAPI.RecoverFromMessage	KIP-97 and EIP-191	KIP-97 and EIP-191 (unchanged)

Types of changes

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• Bugfix
• New feature or enhancement
• Others

Checklist

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• Lint and unit tests pass locally with my changes ($ make test)
• I have added tests that prove my fix is effective or that my feature works
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• Any dependent changes have been merged and published in downstream modules

Related issues

Further comments

• This PR aims to deprecate the KIP-97 in favor of the widely accepted EIP-191. Ethereum tools compatibility should improve.
• A EIP-155-style cross-chain replay protection can be achieved by using EIP-712, not by using KIP-97.
• The KIP-97 signature and verify will still be available via caver-js and caver-java
  • caver-js keyring.signMessage, utils.recover
  • caver-java AbstractKeyring.signMessage​, Utils.recover
• See tests here: QA for v1.0.1 #14 (comment)