Add support for a domain transfer request superuser EPP extension

Allow superusers to change the transfer period to zero years and allow
superusers to change the automatic transfer length.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=167598314

java/google/registry/model/domain/superuser/SuperuserExtension.java

@@ -0,0 +1,23 @@
+// Copyright 2017 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.
+
+package google.registry.model.domain.superuser;
+
+import google.registry.model.ImmutableObject;
+import google.registry.model.eppinput.EppInput.CommandExtension;
+import javax.xml.bind.annotation.XmlTransient;
+
+/** Base class for superuser EPP extensions. */
+@XmlTransient
+public abstract class SuperuserExtension extends ImmutableObject implements CommandExtension {}