696: Allow software updates to start from version 0 or 1 r=dnadales a=dcoutts
It does not really matter if application versions start from 0 or 1, and the old cardano-sl code allows both. An initial version 0 has been used on the public testnet (but not mainnet), and so it is useful to agree with the old cardano-sl and declare that to be valid.
Also update the comments for the function that does the validation of the versions. The existing comments says that we allow keeping the same version, but the existing code and the formal spec always require an increment of exactly 1. So we correct the comment.
- [x] bring the formal and executable specs in line on the 0 vs 1 issue.