Changed bare image of geometry.

The image that was used before as an example geometry is actually the worst one of the set of pictures... 

Here is a link to the bare geometry, as seen by GMSH when opening the iges file:

https://www.dropbox.com/s/3we64ldns0lx3yl/step-54.bare.png

I changed the name in intro.dox. The file above should be copied on the web server...