Clean up the CSS

[maehler]

There is a lot of unused stuff in the stylesheets that should be cleaned out in order to improve readability.

[dilema]

Big cleaning made in add8e3f.
Might be some remnant and also used class removed (unlikely). I let the issue open because I'd like to:

• Reorganize the stylesheet so it follow the html content organization
• Add whitespace consistency (now it's a mix of tab and space)
• (Rename the class for clearer semantic)
• Add a reset
• Pass CSS validator