More tweaks to styling

[neilb]

• I'd missed one change from my hacking: the footer elements are now grouped with a div. The CSS for that was in the previous pull request.
• transparent background for the stars .png's so they'll work on a non-white background
• turn off underlines in most anchors, so the header won't look quite so goofy
• tweaked the look of the header, according to Ask's lack of taste :-)
• ran optipng on the star png's I'd modified (thanks for the tip)