types.NewCommit (#3275)

* types.NewCommit

* use types.NewCommit everywhere

* fix log in unsafe_reset

* memoize height and round in constructor

* notes about deprecating toVote

* bring back memoizeHeightRound

node/node_test.go

@@ -260,7 +260,7 @@ func TestCreateProposalBlock(t *testing.T) {
 		evidencePool,
 	)
 
-	commit := &types.Commit{}
+	commit := types.NewCommit(types.BlockID{}, nil)
 	block, _ := blockExec.CreateProposalBlock(
 		height,
 		state, commit,