fix order of BlockID and Timestamp in Vote and Proposal (#3078)

* Consistent order fields of Timestamp/BlockID fields in CanonicalVote and
CanonicalProposal

* update spec too

* Introduce and use IsZero & IsComplete:
 - update IsZero method according to spec and introduce IsComplete
 - use methods in validate basic to validate: proposals come with a
 "complete" blockId and votes are either complete or empty
 - update spec: BlockID.IsNil() -> BlockID.IsZero() and fix typo

* BlockID comes first

* fix tests

docs/spec/blockchain/blockchain.md

@@ -109,10 +109,6 @@ Tendermint uses the
 [Google.Protobuf.WellKnownTypes.Timestamp](https://developers.google.com/protocol-buffers/docs/reference/csharp/class/google/protobuf/well-known-types/timestamp)
 format, which uses two integers, one for Seconds and for Nanoseconds.
 
-NOTE: there is currently a small divergence between Tendermint and the
-Google.Protobuf.WellKnownTypes.Timestamp that should be resolved. See [this
-issue](https://github.com/tendermint/go-amino/issues/223) for details.
-
 ## Data
 
 Data is just a wrapper for a list of transactions, where transactions are

docs/spec/blockchain/encoding.md

@@ -301,8 +301,8 @@ type CanonicalVote struct {
 	Type      byte
 	Height    int64            `binary:"fixed64"`
 	Round     int64            `binary:"fixed64"`
-	Timestamp time.Time
 	BlockID   CanonicalBlockID
+	Timestamp time.Time
 	ChainID   string
 }
 ```