Add "Bind" and "Unbind" methods

New methods allow to bind and unbind public keys
with the owner, therefore the user can store and
access data with the key, that does not related
to the wallet.

neofs_contract.go

@@ -35,6 +35,7 @@ const (
 	candidatesKey         = "candidates"
 	cashedChequesKey      = "cheques"
 	blockDiff             = 20 // change base on performance evaluation
+	publicKeySize         = 33
 )
 
 func Main(op string, args []interface{}) interface{} {
@@ -228,6 +229,29 @@ func Main(op string, args []interface{}) interface{} {
 			runtime.Notify("Cheque", id, user, amount, lockAcc)
 		}
 
+		return true
+	case "Bind", "Unbind":
+		if len(args) < 2 {
+			panic("binding: bad arguments")
+		}
+
+		user := args[0].([]byte)
+		if !runtime.CheckWitness(user) {
+			panic("binding: you should be the owner of the wallet")
+		}
+
+		var keys [][]byte
+		for i := 1; i < len(args); i++ {
+			pub := args[i].([]byte)
+			if len(pub) != publicKeySize {
+				panic("binding: incorrect public key size")
+			}
+
+			keys = append(keys, pub)
+		}
+
+		runtime.Notify(op, user, keys)
+
 		return true
 	case "InnerRingUpdate":
 		data := args[0].([]byte)