types: CommitVotes struct as last step towards #1648 (#3298)

* VoteSignBytes builds CanonicalVote

* CommitVotes implements VoteSetReader

- new CommitVotes struct holds both the Commit and the ValidatorSet and
  implements VoteSetReader
- ToVote takes a ValidatorSet

* fix TestCommit

* use CommitSig.BlockID

Commits may include votes for a different BlockID, could be nil,
or different altogether. This means we can't use `commit.BlockID`
for reconstructing the sign bytes, since up to -1/3 of the commits
might be for independent BlockIDs. This means CommitSig will need to
include an indicator for what BlockID it signed - if it's not the
committed one or nil, it will need to include it fully in order to be
verified. This is unfortunate but unavoidable so long as we include
votes for non-committed BlockIDs (which we do to track validator
liveness)

* fixes from review

* remove CommitVotes. CommitSig contains address

* remove commit.canonicalVote method

* toVote -> getVote, takes valIdx

* update adr-025

* commit.ToVoteSet -> CommitToVoteSet

* add test

* fix from review

consensus/state.go

@@ -484,16 +484,7 @@ func (cs *ConsensusState) reconstructLastCommit(state sm.State) {
 		return
 	}
 	seenCommit := cs.blockStore.LoadSeenCommit(state.LastBlockHeight)
-	lastPrecommits := types.NewVoteSet(state.ChainID, state.LastBlockHeight, seenCommit.Round(), types.PrecommitType, state.LastValidators)
-	for _, precommit := range seenCommit.Precommits {
-		if precommit == nil {
-			continue
-		}
-		added, err := lastPrecommits.AddVote(seenCommit.ToVote(precommit))
-		if !added || err != nil {
-			panic(fmt.Sprintf("Failed to reconstruct LastCommit: %v", err))
-		}
-	}
+	lastPrecommits := types.CommitToVoteSet(state.ChainID, seenCommit, state.LastValidators)
 	if !lastPrecommits.HasTwoThirdsMajority() {
 		panic("Failed to reconstruct LastCommit: Does not have +2/3 maj")
 	}