Add sitemap support in bundled Heritrix3

Links to sitemaps can be present in robots.txt files.
e.g.

Sitemap: http://kursuskatalog.au.dk/sitemap.xml

and

User-Agent: *
Disallow: /da/error/
Disallow: /en/error/
Disallow: /image_client
Disallow: /da/soeg/
Sitemap: http://www.kb.dk/da/Sitemap.jsp
Sitemap: http://www.kb.dk/en/Sitemap.jsp

We should enable Heritrix3 to extract these sitemap links and put them into the h3 queues for harvesting. When harvested they should be parsed by a SiteMapExtractor and the found links put into the h3 queues