Cert: Display identity’s blockstamp and date into confirmation message

Cf: https://forum.duniter.org/t/cesium-nouvelle-version-v1-3-6/5868/24?u=moul

When certifying, Silkaj takes the first identity found which equals passed identity. In some rare case, someone might publish again its identity, and two identities with same id and same pubkey, but not same blockstamp may exist on the network. In that case, the first one found could be the identity expiring.

Silkaj could ask to choose between those two identities thanks to a prompt with the date into the blockstamp.