[#770] pkg/morph/event: Add notary request preparator

Add preparator for notary requests. Is parses
raw notary requests, checks if it should be
handled by Alphabet node. If handling is required,
returns `NotaryEvent` that contains information
about contract scripthash, method name and
arguments of the call.

Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>

pkg/morph/event/opcodes.go

@@ -0,0 +1,21 @@
+package event
+
+import "github.com/nspcc-dev/neo-go/pkg/vm/opcode"
+
+// Op is wrapper over Neo VM's opcode
+// and its parameter.
+type Op struct {
+	code  opcode.Opcode
+	param []byte
+}
+
+// Code returns Neo VM opcode.
+func (o Op) Code() opcode.Opcode {
+	return o.code
+}
+
+// Param returns parameter of wrapped
+// Neo VM opcode.
+func (o Op) Param() []byte {
+	return o.param
+}