[#421] morph/client: Add role getter from designate contract

RoleManagement native contract (ex designate contract) stores list
of keys per role. Main net uses NeoFSAlphabet role to store keys of
alphabet nodes of inner ring. Side chain uses the same role to store
keys of all inner ring nodes, including alphabet.

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

pkg/morph/client/constructor.go

@@ -105,12 +105,18 @@ func New(key *ecdsa.PrivateKey, endpoint string, opts ...Option) (*Client, error
 		return nil, err
 	}
 
+	designate, err := cli.GetNativeContractHash(nativenames.Designation)
+	if err != nil {
+		return nil, err
+	}
+
 	return &Client{
 		logger:       cfg.logger,
 		client:       cli,
 		acc:          account,
 		gas:          gas,
 		neo:          neo,
+		designate:    designate,
 		waitInterval: cfg.waitInterval,
 	}, nil
 }