Set cache control to 'no-cache' for unpublished data-sets [#72069960]

- Adds test to ensure unpublished data-sets are not cached
- Sets cache control to 'no-cache' based on reading through things like http://stackoverflow.com/questions/1046966/whats-the-difference-between-cache-control-max-age-0-and-no-cache?answertab=votes#tab-top
- The `fetch` method could possibly do with being refactored so that we use our `cache_control` module methods to serve the fetch response separately. It's probably fine for the context of this story though (https://www.pivotaltracker.com/story/show/72069960)