Sandbox

@drsnyder 
Removed media_types per our discussion this morning, and added /static/sandbox.html, which lets you play around with different thumbnailing options. This depends on a path starting with ```/bucket/a/ab/``` being able to fetch one of the images in ```image-samples/```, similar to ```vignette.util.integration/default-map```
We could generate this dynamically in clojure :).