--cosigner option? #14
Description
Related to #12 & #13 & to LetheKit:
I think one of the most common uses for us (Blockchain Commons) is to get the 48h/0h/0h/2h cosigner derivation into the short text & a UR QR form (with the optional label and birthday), suitable for offering or receiving as part of a Policy Map -> Account Map process. Thus could maybe be a --cosigner shortcut option for keytool.
Currently I don't think we can use crypto-account for this, so we need to puzzle that through.
Note that this does not solve the problem of cosigner reuse: later we figure out a good way to have different cosigners for different Account Maps we'll need to puzzle that through as well. But a simple --cosigner option will help a lot.
Related, we may want to explicitly add this 48h/0h/0h/2h cosigner UR to LetheKit, as it long-term may be the most common export option from an offline seed.