[Bf-webcontent] Added dynamic sitemap

[Bart Veldhuizen]

Hi,

I sometimes got a bit confused about what is where on the website, so I 
thought it was time to add a sitemap:

http://www.blender3d.org/cms/Sitemap.259.0.html

It's dynamically generated, but like all HTML on the site it will have 
to be republished when something in the site structure changes.

I have also added a link to the sitemap from the search page.

It might look nicer if we had a bit more space to put our content in but 
hey, we'll keep that in mind for the new site :-)

Bart