Add media service to image rewriting

Waiting on a NGINX config change for this to go through.
Images from the media service need to be rewritten with `/media` prefixed as discussed with @phamann.

![Cameras](http://gifshost.com/012012/1327341659_lightning_caught_on_camera.gif)
Is this in order to only pass optimisable images through your service? If so, maybe a whitelist would be more appropriate? Do you support all formats apart from GIF (e.g. PNG, SVG, etc)?