add background gradient, delete background images, change body max-width

This affects two small css issues:

- https://github.com/mozfr/transvision/issues/59
Max-width deleted. Now the tables take the entire screen size.

- https://github.com/mozfr/transvision/issues/60
Using CSS3 background gradient instead images. 
Change link colors to adapt it to mozilla guidelines ( http://www.mozilla.org/en-US/styleguide/websites/sandstone/colors/ )