Improved help system

Improve yelp for both GNOME and Ubuntu documentation so that it checks for newer documentation if an internet connection is available. This could be useful if there are, for example, updated documents or documents in the users' language of choice available. There could be also a knowledgebase (the knowledgebase regarding GNOME should be hosted at GNOME and integrated with upstream) be created with tags so that when the user searchs in yelp (example: how can i change my desktop background), he is also displayed information that has been added by users (of course there should be good QA).

As an extra, tags could be added to help.ubuntu.com, and it should be searchable via yelp, too.

Another idea that I have is that (mainly GNOME docus) can be tagged to the GNOME version, like if nothing has changed in 2.20, the same document is displayed in version 2.20 if it is tagged with 2.20, also. If something has changed, a new document is being created which is only tagged with 2.20.