Ability to get contractID of person who sent a GIMessage (innerSigningContractID() function)

[taoeffect]

Problem

In PR #2046 there is the desire to display who sent a GIMessage that resulted in an error:

It seems like there's no simple way to get this information from a GIMessage.

Solution

Implement innerSigningContractID() on GIMessage that returns this info if available as a string, otherwise null.

Update the code here (see screenshot above if link doesn't work) to restore the contractID information for that notification so that we can know what user sent the failing message.