[Marketing] A couple material updates

Just an FYI - I've just got the main OSGeo Brochure updated with our latest
project stack, and have a bunch being printed for FOSS4G. I also made up a
(very simple) sponsorship thank you page for posting at our events. I will
have plenty of these for folks to take copies of at FOSS4G. For printing at a
later date, you can find them in SVN: