Add basic AllocationToken validation/redemption for domain creates

The next step is to add them for domain checks as well (which is simpler
because it doesn't involve validation).

This requires the addition of a TrimWhitespaceAdapter for XML JAXB objects,
which will prove useful for other @XmlValue attributes in the future.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=181526726

java/google/registry/xml/TrimWhitespaceAdapter.java

@@ -0,0 +1,48 @@
+// 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.xml;
+
+import com.google.common.base.CharMatcher;
+import javax.annotation.Nullable;
+import javax.xml.bind.annotation.adapters.XmlAdapter;
+
+/**
+ * {@link XmlAdapter} which trims all whitespace surrounding a String.
+ *
+ * <p>This is primarily useful for <code>@XmlValue</code>-annotated fields in JAXB objects, as XML
+ * values can commonly be formatted like so:
+ *
+ * <pre>{@code
+ *   &lt;ns:tag&gt;
+ *     XML value here.
+ *   &lt;/ns:tag&gt;
+ * }</pre>
+ */
+public class TrimWhitespaceAdapter extends XmlAdapter<String, String> {
+
+  private static final CharMatcher WHITESPACE = CharMatcher.anyOf(" \t\r\n");
+
+  @Override
+  @Nullable
+  public String unmarshal(@Nullable String value) {
+    return (value == null) ? null : WHITESPACE.trimFrom(value);
+  }
+
+  @Override
+  @Nullable
+  public String marshal(@Nullable String str) {
+    return str;
+  }
+}