Sparklines

* Uses the [sparklines](https://github.com/stephanfowler/ophan-sparklines) image service, as deployed [here](http://sparklines.ophan.co.uk/?graphs=guardian:009,google:090,other:09f&showStats=1&showHours=1&width=100&height=40).
* Markers: orange for first added, grey for moved, green for edited. These are experimental and do not yet distinguish between live and draft changes.
* Adds a sparkline for overall traffic the selected front.


![fronts-tool](https://f.cloud.github.com/assets/1147913/1995423/95878a1c-8504-11e3-88c9-919006b2bb4a.png)