Adds DnsWriter that implements DNS UPDATE protocol

* DnsUpdateWriter publishes changes to NS, DS, A, AAAA records
  for domains/hosts as appropriate using RFC 2136 DNS UPDATE protocol
* Static configuration separate from RegistryConfig
* Include dnsjava library as new third party dependency
  to generate DNS protocol messages
* Expose /_dr/task/writeDns in RegistryTestServer
* Currently not included in BackendComponent

java/com/google/domain/registry/dns/writer/dnsupdate/DnsUpdateConfigModule.java

@@ -0,0 +1,54 @@
+// Copyright 2016 The Domain Registry 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.
+
+package com.google.domain.registry.dns.writer.dnsupdate;
+
+import com.google.domain.registry.config.ConfigModule.Config;
+
+import org.joda.time.Duration;
+
+import dagger.Module;
+import dagger.Provides;
+
+@Module
+public class DnsUpdateConfigModule {
+
+  /**
+   * Host that receives DNS updates from the registry.
+   * Usually a "hidden master" for the TLDs.
+   */
+  @Provides
+  @Config("dnsUpdateHost")
+  public static String provideDnsUpdateHost() {
+    return "localhost";
+  }
+
+  /**
+   * Timeout on the socket for DNS update requests.
+   */
+  @Provides
+  @Config("dnsUpdateTimeout")
+  public static Duration provideDnsUpdateTimeout() {
+    return Duration.standardSeconds(30);
+  }
+
+  /**
+   * The DNS time-to-live (TTL) for resource records created by the registry.
+   */
+  @Provides
+  @Config("dnsUpdateTimeToLive")
+  public static Duration provideDnsUpdateTimeToLive() {
+    return Duration.standardHours(2);
+  }
+}