[#326] morph/balance: Provide interface to "transferX" method's invocations

Implement TransferX method on Balance contract client. Implement TransferX
method on Balance client's wrapper that encapsulates it's TransferX call.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/morph/client/balance/wrapper/transfer.go

@@ -0,0 +1,40 @@
+package wrapper
+
+import (
+	"github.com/nspcc-dev/neofs-api-go/pkg/owner"
+	"github.com/nspcc-dev/neofs-node/pkg/morph/client/balance"
+	"github.com/pkg/errors"
+)
+
+// TransferPrm groups parameters of TransferX method.
+type TransferPrm struct {
+	Amount int64
+
+	From, To *owner.ID
+
+	Details []byte
+}
+
+// TransferX transfers Amound of GASe-12 from p.From to p.To
+// with details p.Details through smart contract call.
+func (w *Wrapper) TransferX(p TransferPrm) error {
+	from, err := owner.ScriptHashBE(p.From)
+	if err != nil {
+		return errors.Wrap(err, "invalid sender")
+	}
+
+	to, err := owner.ScriptHashBE(p.To)
+	if err != nil {
+		return errors.Wrap(err, "invalid recipient")
+	}
+
+	// prepare invocation arguments
+	args := balance.TransferXArgs{}
+	args.SetSender(from)
+	args.SetRecipient(to)
+	args.SetAmount(p.Amount)
+	args.SetDetails(p.Details)
+
+	// invoke smart contract call
+	return w.client.TransferX(args)
+}