Feature/travelshed labels

![screen shot 2014-12-22 at 2 43 14 pm 2](https://cloud.githubusercontent.com/assets/1977405/5530047/7d34036a-89e9-11e4-8f5a-3bbdb19793da.png)
![screen shot 2014-12-22 at 2 43 11 pm 2](https://cloud.githubusercontent.com/assets/1977405/5530049/80f68c52-89e9-11e4-9fb5-faefd6591ecc.png)


This changeset includes the addition of a legend for the jobs indicator, some logic to hide said legend and its data (by default), an endpoint for min/max values on the jobs indicator, and a small fix to the travelshed calculation.