Improved color picking and abstract out getting the JSON.

* Change color picking so all items under the source level are shades of the same color.
* Moved the code for retrieving the JSON into a function.
* Changed the d3.json call to $.getJSON so we can easily return a promise.
* Reduced duplication by no longer need two different success handler functions.
Merge branch 'master' into gh-pages

* master:
  Improved color picking and abstract out getting the JSON.