StateDB ZKInputs generation compatible with circom

- Add SignatureConstant to L1Tx.TxCompressedData
- ZKInputs generation works initial version working and compatible with circom Hermez circuit
    - Lots of small updates for circuits compatibility
- Update version (with new changes) of `go-iden3-crypto` & `go-merkletree`

common/tx.go

@@ -34,6 +34,13 @@ const (
 	TxIDLen = 12
 )
 
+var (
+	// SignatureConstantBytes contains the SignatureConstant in byte array
+	// format, which is equivalent to 3322668559 as uint32 in byte array in
+	// big endian representation.
+	SignatureConstantBytes = []byte{198, 11, 230, 15}
+)
+
 // TxID is the identifier of a Hermez network transaction
 type TxID [TxIDLen]byte