Add and wire up the AllocationTokenExtension XML class

The extension itself isn't used for anything yet; allocation tokens can be
passed for domain creates and checks but are ignored if present. This will
be changed in a subsequent CL that adds AllocationToken entities and related
logic. Usage of this extension in any other EPP flow will throw an
UnsupportedExtensionException.

The relevant spec is https://tools.ietf.org/html/draft-gould-allocation-token-04

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=181343188

java/google/registry/model/domain/token/package-info.java

@@ -0,0 +1,31 @@
+// 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.
+
+@XmlSchema(
+  namespace = "urn:ietf:params:xml:ns:allocationToken-1.0",
+  xmlns =
+      @XmlNs(
+        prefix = "allocationToken",
+        namespaceURI = "urn:ietf:params:xml:ns:allocationToken-1.0"
+      ),
+  elementFormDefault = XmlNsForm.QUALIFIED
+)
+@XmlAccessorType(XmlAccessType.FIELD)
+package google.registry.model.domain.token;
+
+import javax.xml.bind.annotation.XmlAccessType;
+import javax.xml.bind.annotation.XmlAccessorType;
+import javax.xml.bind.annotation.XmlNs;
+import javax.xml.bind.annotation.XmlNsForm;
+import javax.xml.bind.annotation.XmlSchema;