public datasets visible when not logged in

[tcnichol]

This is the front end component of making public datasets and files visible if you are not logged in. To be done after the back end portion.

[tcnichol]

This issue will now involve some changes in the back end as well. Datasets that will be visible only to logged in users are now "Authenticated" and there is a pull request for that, and public datasets are different and are visible when not logged in. This means that there will be a new dataset status and new routes in the back end.