(VDB-929) Minimize storage key lookup bespoke code

- Extract shared namespace for looking up and hashing keys
- Require storage transformers only to implement a loader that
  associates known keys with metadata
- Move key loader/lookup utils to utils directory to avoid
  multiple "storage" packages in imports

libraries/shared/mocks/storage_keys_loader.go

@@ -0,0 +1,39 @@
+// VulcanizeDB
+// Copyright © 2019 Vulcanize
+
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package mocks
+
+import (
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/vulcanize/vulcanizedb/libraries/shared/storage/utils"
+	"github.com/vulcanize/vulcanizedb/pkg/datastore/postgres"
+)
+
+type MockStorageKeysLoader struct {
+	LoadMappingsCallCount int
+	LoadMappingsError     error
+	SetDBCalled           bool
+	StorageKeyMappings    map[common.Hash]utils.StorageValueMetadata
+}
+
+func (loader *MockStorageKeysLoader) LoadMappings() (map[common.Hash]utils.StorageValueMetadata, error) {
+	loader.LoadMappingsCallCount++
+	return loader.StorageKeyMappings, loader.LoadMappingsError
+}
+
+func (loader *MockStorageKeysLoader) SetDB(db *postgres.DB) {
+	loader.SetDBCalled = true
+}

libraries/shared/mocks/storage_keys_lookup.go

@@ -18,22 +18,21 @@ package mocks
 
 import (
 	"github.com/ethereum/go-ethereum/common"
-
 	"github.com/vulcanize/vulcanizedb/libraries/shared/storage/utils"
 	"github.com/vulcanize/vulcanizedb/pkg/datastore/postgres"
 )
 
-type MockMappings struct {
+type MockStorageKeysLookup struct {
 	Metadata     utils.StorageValueMetadata
 	LookupCalled bool
 	LookupErr    error
 }
 
-func (mappings *MockMappings) Lookup(key common.Hash) (utils.StorageValueMetadata, error) {
+func (mappings *MockStorageKeysLookup) Lookup(key common.Hash) (utils.StorageValueMetadata, error) {
 	mappings.LookupCalled = true
 	return mappings.Metadata, mappings.LookupErr
 }
 
-func (*MockMappings) SetDB(db *postgres.DB) {
+func (*MockStorageKeysLookup) SetDB(db *postgres.DB) {
 	panic("implement me")
 }