Complete Extras section for YUI CSS Website

[tilomitra]

References Trac #2533191.

The extras section is a little half-baked right now. We want the following features:

• List a curated collection of gallery modules that leverage YUI CSS in some shape or form.
• Pull in the module info through Github on process start

The current status of this ticket can be found here:
pure-css/pure-site#14

[ericf]

I think this should be integrated with Bower, or at least Bower serves as the fetching mechanism since we don't want to host these on our CDN.