[MNG-8073] Adding ASL2 header to XSD files (#1499)

Using latest modello release and putting license
into POM.

---

https://issues.apache.org/jira/browse/MNG-8073

pom.xml

@@ -664,6 +664,26 @@ under the License.
         <plugin>
           <groupId>org.codehaus.modello</groupId>
           <artifactId>modello-maven-plugin</artifactId>
+          <!-- TODO: Remove with parent 43 -->
+          <version>2.4.0</version>
+          <configuration>
+            <licenseText>Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you 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.</licenseText>
+          </configuration>
           <executions>
             <execution>
               <id>modello-site-docs</id>