citeme for journals for #60

* adds a dialogue when a user clicks to download code or data which reminds them to cite code and data. The dialogue also has a link, so the user doesn't need to click to dismiss the dialogue to be able to continue to their task.
* displays citation information on the main details page as well as the dialogue
* Is a hack -- this only adds some additional columns to the Article model, appropriate for journal citations.
* TODO -- store bibjson information about the Article and use bibjson formatting code to render citation for any item type.