[#973] ir: Listen and process Put/Delete events of Subnet contract

Define notification events, implement parsers. Add morph client of
Subnet contract. Listen, verify and approve events in Inner Ring app.

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

pkg/morph/client/subnet/delete.go

@@ -0,0 +1,40 @@
+package morphsubnet
+
+import (
+	"github.com/nspcc-dev/neo-go/pkg/util"
+	"github.com/nspcc-dev/neofs-node/pkg/morph/client"
+)
+
+// DeletePrm groups parameters of Delete method of Subnet contract.
+type DeletePrm struct {
+	cliPrm client.InvokePrm
+
+	args [1]interface{}
+}
+
+// SetTxHash sets hash of the transaction which spawned the notification.
+// Ignore this parameter for new requests.
+func (x *DeletePrm) SetTxHash(hash util.Uint256) {
+	x.cliPrm.SetHash(hash)
+}
+
+// SetID sets identifier of the subnet to be removed in a binary NeoFS API protocol format.
+func (x *DeletePrm) SetID(id []byte) {
+	x.args[0] = id
+}
+
+// DeleteRes groups resulting values of Delete method of Subnet contract.
+type DeleteRes struct{}
+
+// Delete removes subnet though the call of the corresponding method of the Subnet contract.
+func (x Client) Delete(prm DeletePrm) (*DeleteRes, error) {
+	prm.cliPrm.SetMethod("delete")
+	prm.cliPrm.SetArgs(prm.args[:]...)
+
+	err := x.client.Invoke(prm.cliPrm)
+	if err != nil {
+		return nil, err
+	}
+
+	return new(DeleteRes), nil
+}