Move static PNG/SVG files into static/

This prepares the way for bringing over the dynamic shields-as-a-service
code that was developed under the code name "badgr.co."
Add shielded as a submodule under vendor/

This is the CLI we're using right now to generate PNGs. There's a Go
version in the works that is much faster. For now we're going to launch
with this one. We've got a caching strategy in place to mitigate the
slowness.
Initial import of Shields.io code

I wrote this in another repo, and now I've cleaned it up to import here
as Shields.io.
Merge pull request #44 from gittip/shields.io

Import code from badgr.co