Pkgcloud integration

This sets up some initial pkgcloud integration to shunt the images off to a CDN.
Alternate Strategy for cdnUrl would come after defining `server`:

```javascript
server.use(function(req, res, next) {
  var cdnUrl;

  // if we already have the url, just put it in the request, and then continue
  if (cdnUrl) {
    req.cdnUrl = cdnUrl;
    next();
    return;
  }

  // note, this would create a latency for the first request
  client.getContainer(containerName, function(err, container) {
    if (err) { next(err); return; }
    
    cdnUrl = container.cdnSslUri;
    req.cdnUrl = cdnUrl;
    next();
    return;
  });
}
```