[#62] morph: List morph rules chains by traversing iterator

* Make `ListMorphRuleChains` methods use `commonclient.ReadIteratorItems`.
* Make `NewContractStorage` receive `rpcInvoker` to initialize `Invoker`
  within `listChains`.
* Iterators are used because listing by `ListChainsByPrefix` may cause
  stack overflow from neo-go side (len(items) > 1024).

Signed-off-by: Airat Arifullin <aarifullin@yadro.com>

pkg/morph/policy/policy_contract_storage.go

@@ -14,10 +14,9 @@ import (
 	"github.com/google/uuid"
 	"github.com/nspcc-dev/neo-go/pkg/neorpc/result"
 	"github.com/nspcc-dev/neo-go/pkg/rpcclient/actor"
+	neoinvoker "github.com/nspcc-dev/neo-go/pkg/rpcclient/invoker"
 	"github.com/nspcc-dev/neo-go/pkg/util"
 	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
-
-	neoinvoker "github.com/nspcc-dev/neo-go/pkg/rpcclient/invoker"
 	"github.com/nspcc-dev/neo-go/pkg/wallet"
 )