Adding "group" notion and image/video sitemap

This update is backward.

Now you can to add a title to sitemap file, and adding image/photo sitemap, based on sitemaps google :
- Image :
http://support.google.com/webmasters/bin/answer.py?hl=en&answer=178636
- Video :
http://support.google.com/webmasters/bin/answer.py?hl=en&answer=80472