Hmm, I think we should probably standardize against the restify errors (since those would be the hardest to change, I'm assuming).

So for 404, something like 
```json
{"code":"NotFound", message:"[Badge|Issuer|Program] with slug `xyz-slug` could not be found"}
```

And for 400 errors, maybe
```json
{"code":"ValidationErrors", "message":"Failed validation", "details":[{"message":"String is not in range","field":"Name"}]}
```