Implement ImagesController

RFC @sobering and @johnTurknett — This PR is still a *WORK IN PROGRESS* so please do not merge.  I wanted to get something started in the hopes of building some momentum, this is the beginning of the `ImagesController`.

This PR is progress towards closing out #11.
Just a placeholder now, this should enable us to keep all of the business logic out of controllers.  Furthermore, this will allow @jamesbrink to eventually write his own local adapter to use the `ImageMagick` API directly without the need for background workers.