Add a DAO for RegistryLock objects (#290)

* Add a DAO for RegistryLock objects

* Add an index on verification code and remove old file

* Move to v4

* Use camelCase in index names

* Javadoc fixes

* Allow alteration of RegistryLock objects in-place

* save, load-modify, read in separate transactions

* Change the creation timestamp to be a CreateAutoTimestamp

db/src/main/resources/sql/flyway/V4__registry_lock_add_index_on_verification_code.sql

@@ -0,0 +1,16 @@
+-- Copyright 2019 The Nomulus Authors. All Rights Reserved.
+--
+-- Licensed under the Apache License, Version 2.0 (the "License");
+-- you may not use this file except in compliance with the License.
+-- You may obtain a copy of the License at
+--
+--     http://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing, software
+-- distributed under the License is distributed on an "AS IS" BASIS,
+-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+-- See the License for the specific language governing permissions and
+-- limitations under the License.
+
+    create index if not exists idx_registry_lock_verification_code ON "RegistryLock"
+       using btree (verification_code);