Return multisig info in APIs

[zone117x]

Ref #193 (comment)

Multisig transactions have a few additional fields that can be returned.

@aulneau @hstove any input on what might be useful?

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[sabbyanandan]

@aulneau @hstove: A friendly follow-up. Any details about the use case or the need for the additional attributes would be appreciated.