[#505] neofsid: Implement wrapper over contract client

Implement wrapper over NeoFS ID contact's client which allows to which
allows you to conveniently interact with the contract. Implement
`AccountKeys` method for getting a list of keys by account ID.

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

pkg/morph/client/neofsid/wrapper/client.go

@@ -0,0 +1,23 @@
+package neofsid
+
+import (
+	"github.com/nspcc-dev/neofs-node/pkg/morph/client/neofsid"
+)
+
+// ClientWrapper is a wrapper over NeoFS ID contract
+// client which provides convenient methods for
+// working with a contract.
+//
+// Working ClientWrapper must be created via Wrap.
+type ClientWrapper neofsid.Client
+
+// Wrap creates, initializes and returns the ClientWrapper instance.
+//
+// If c is nil, panic occurs.
+func Wrap(c *neofsid.Client) *ClientWrapper {
+	if c == nil {
+		panic("neofs ID client is nil")
+	}
+
+	return (*ClientWrapper)(c)
+}