Account constructor
Implementation
Account(String ed25519AccountId, int sequenceNumber,
{int muxedAccountMed25519Id}) {
_accountId = checkNotNull(ed25519AccountId, "keypair cannot be null");
_mSequenceNumber =
checkNotNull(sequenceNumber, "sequenceNumber cannot be null");
_muxedAccount = MuxedAccount(ed25519AccountId, muxedAccountMed25519Id);
}