Embed-friendly dashboards

We need to provide routing for rendering web pages with only the actual dashboards (No diamondash navbar or anything else). This will be used to embed a diamondash dashboard in another html document (possibly using `<iframe>`, `<object>` or `<embed>`). For the short term, the aim is simple itegration of diamondash with [vumi-go](https://github.com/praekelt/vumi-go) .