Some website tweaks

A couple of minor things bothered me about the current site, have fixed
them in a local copy and published the changes:

http://sites.shishnet.org:8088
https://github.com/shish/pgadmin-www

Specifically:
- CSS has been deduplicated (one base file with pretty much everything
in it, then rtl and ltr files which contain only the
text-direction-specific tweaks)
- Top menus made all boxy, rather than part-boxy-part-listy
- The background colour boxes when hovering over the top menu entries
were very tightly wrapped around the text; I've made them fill the whole box
- Screenshots index has them side-by-side instead of a long list with
lots of whitespace and scrolling
- Link to Suse 10 XGL screenshot commented out, because 2005 called and
asked to have its embarassing photos removed :P

I'm also considering updating the screenshots themselves, because
Windows XP and 90's-style Solaris desktops at 800x600 don't exactly
scream "this software project is alive and up-to-date", but that's more
effort so I figured I'd see if anyone cares first

     -- Shish