Adding basic framework to support Featured Articles for sponsors.

Let me preface this by saying that this is 100% temporary ugly hacky
throwaway code that should not survive past this conference. It's a
one-off thing that lets us get the content online quickly with minimal
fuss. Do let me know if there's an equally trivial better way; but I
don't think it's worth doing "The Right Thing" here at this point.

This change adds four static templates -- one for each of our Diamond
and Gold sponsors -- and exposes them under the /sponsors/featured/ URL
tree. The sponsor names are hardcoded, as is the featured article content.

Still to do: actually expose these pages somewhere, e.g. via top-menu
dropdown, link from sponsor description, or elsewhere.
Merge pull request #115 from felixc/add-featured-sponsor-articles

Adding basic framework to support Featured Articles for sponsors.