signMessage abstract method
Sign a message for method (personal_sign, eth_sign,
eth_signTypedData*). Called after dialog confirmation.
method is the JSON-RPC method, from is the claimed signer address,
message is the raw payload (hex string or typed data), password
is optional for personal_sign.
Implementation
Future<String> signMessage(
String method,
String from,
dynamic message,
String password,
);