Issue #2249723 by andrei.dincu: Start XmlSitemapTestHelper class
Issue #2249723 by andrei.dincu: Create XmlSitemapRobotsTxtIntegrationTest class
Issue #2249723 by andrei.dincu: Create XmlSitemapFunctionalTest class
Issue #2249723 by andrei.dincu: Create XmlSitemapUnitTest class