Don't set signing address if signer is anon

[zupzup]

If we're not anon in general, but anon holder of a bill, we should not set the signing address

                    endorser: if holder_is_anon {
                        // if holder is anon, we need to continue as anon
                        signer_public_data.as_anon().into()
                    } else {
                        signer_public_data.clone().into()
                    },

This check needs to apply to

                    signing_address: signer_public_data.postal_address(),

And also, the

                    signatory: signing_keys.signatory_identity,

signatory name needs to be Bearer in that case. (or rather, not set)

as well.