[r0.0.75] Group refactoring

collorg.group.group now inherits from collorg.communication.blog.post. It
allows to deal with groups as we do with posts.

* Map of the site has been improved.
* Map is now accessible for every post.
  [WARN] It is only visible if cog_oid == cog_enviroment.

TODO
* Make user inherit from collorg.communication.blog.post.