Initial work towards new "html-fiveish" template

The new design is an experiment with a few things:

-   Using floats and fixed elements to fill large screens without
    multiple columns
-   Trying to make something that can later be easily turned into a
    mobile-friendly design (and maybe print friendly too?)
-   Large, clean and modern sans-serif fonts (the old design was
    serif-based)
-   HTML5 semantic tags (this should get backported to the other
    template)
-   Pulling (some) principles from OOCSS
-   Fixing some issues with the HTML and CSS that were bothering me in
    the original design