Candidacy Blocks should carry `HighestSupportedVersion` and `ProtocolParametersHash`

[alexsporn]

If a potential active validator has never been selected, we don't know which is their highest supported protocol version and the protocol parameters hash they would use if selected for the next epoch.

We should add these informations also in the CandidacyAnnouncement and track them in the validator list so that they can be displayed correctly in the frontends. Else this will show protocol version 0 and the empty hash.