[#60] morph/netmap: Implement Epoch method on netmap client wrapper

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

pkg/morph/client/netmap/wrapper/epoch.go

@@ -0,0 +1,19 @@
+package wrapper
+
+import (
+	"github.com/nspcc-dev/neofs-node/pkg/morph/client/netmap"
+	"github.com/pkg/errors"
+)
+
+// Epoch receives number of current NeoFS epoch
+// through the Netmap contract call.
+func (w *Wrapper) Epoch() (uint64, error) {
+	args := netmap.EpochArgs{}
+
+	vals, err := w.client.Epoch(args)
+	if err != nil {
+		return 0, errors.Wrapf(err, "(%T) could not get epoch number", w)
+	}
+
+	return uint64(vals.Number()), nil
+}