Make license header updates configurable (#1047)

The license header plugin was trying to enforce current dates in the header. The headers can still have an old year, so now the plugin is configurable. One can still update license headers using maven command:
mvn clean install -Dlicense.update.dryrun=false -Dlicense.update.copyright=true -DskipTests=true

pom.xml

@@ -37,6 +37,7 @@
       <solr.directory>${project.build.directory}/solr-${solr.version}</solr.directory>
       <licenseName>enterprise</licenseName>
       <license.update.dryrun>true</license.update.dryrun>
+      <license.update.copyright>false</license.update.copyright>
    </properties>
    <modules>
       <module>search-services</module>
@@ -78,7 +79,7 @@
             <configuration>
                <addJavaLicenseAfterPackage>false</addJavaLicenseAfterPackage>
                <organizationName>Alfresco Software Limited</organizationName>
-               <canUpdateCopyright>true</canUpdateCopyright>
+               <canUpdateCopyright>${license.update.copyright}</canUpdateCopyright>
                <failOnMissingHeader>true</failOnMissingHeader>
                <failOnNotUptodateHeader>true</failOnNotUptodateHeader>
                <licenseResolver>classpath://alfresco</licenseResolver>