Support new multisignature registration transaction on commander

[ishantiw]

Description

According to LIP0041, the new multi-signature registration transaction param schema includes property tx.params.signatures where the member public keys sign the message of the transaction and add their signature to this property instead of adding tx.signatures property of the transaction.

This transaction signing of a multi-signature registration transaction needs to be supported in Commander.

Acceptance Criteria

• Should be able to sign a multi-signature registration transaction with the CLI.