Move screenshots pictures on dedicated directory

* It's not css/style part
* Will be used by screenshots page
List screenshots pictures

* Display all pictures listed in /images/screenshots/
* Only "mini" pictures are displayed, targe to full picture
Screenshot on style

* Better with style
Some mistakes on screenshots page

* *AND* is not *and*
* Better to display thumbnail and link to full picture
* Add a clear spacer before flickr block