stargate: migrate types (#670)

* changelog v0.4.0

* stargate: types changes

* msg and handler changes

* validation

* fixes

* more fixes

* more test fixes

* changelog

* changelog

* lint

* rm comment

* lint

* redundant if condition

types/validation.go

@@ -0,0 +1,17 @@
+package types
+
+import (
+	"bytes"
+
+	ethcmn "github.com/ethereum/go-ethereum/common"
+)
+
+// IsEmptyHash returns true if the hash corresponds to an empty ethereum hex hash.
+func IsEmptyHash(hash string) bool {
+	return bytes.Equal(ethcmn.HexToHash(hash).Bytes(), ethcmn.Hash{}.Bytes())
+}
+
+// IsZeroAddress returns true if the address corresponds to an empty ethereum hex address.
+func IsZeroAddress(address string) bool {
+	return bytes.Equal(ethcmn.HexToAddress(address).Bytes(), ethcmn.Address{}.Bytes())
+}