GET /photo returns a random camera, GET /photo.json returns all

`GET /photo.json` returns JSON with URLs to photos from all attached cameras:

As in: (I only have one camera in this machine)

```json
{
  "images": [
    "http://localhost:9393/snap_1_1357951597.jpg"
  ]
}
```

## Goals

* [x] Redirect to random camera on `GET /photo`
* [x] Return all photos in JSON
* [ ] Hubot integration

cc/ @skalnik