Add citation to tutorials

[kelle]

Great idea from @nksaunders: At the end of each tutorial, proved the citation information for packages used. Basically, if one used the same packages as part of doing a published piece of research, show the best way to cite them.

The goal is two fold: 1) We'll want to make it easy to copy and paste the citation and 2) be a nice looking citation in the rendered Jupyter notebook. This might take some work to figure out the best/easiest way to do this.

This might get implemented in the near future on some Kepler tutorials (being hosted on STScI's site) but we'll post links here as we figure out the best way to style these citations.

[nksaunders]

Here is a demo of the work-in-progress implementation for our Kepler tutorials:

To make citing astropy and lightkurve as easy as possible for users, I wrote a short javascript widget that adds a button at the end of tutorials to copy the relevant BibTeX entries to the clipboard.

The buttons are currently hosted on my personal website here. When inserted at the end of a Jupyter Notebook tutorial, it looks like this:

The input cell containing the IPython.display.HTML call will be removed when the html version of the notebook is generated and uploaded. Any feedback is welcome on the style or functionality of the buttons! Should we also include the raw BibTeX in an exposed text area for users to copy manually?

We also plan to render the citations below as they would appear in a journal. It will probably be easiest to manually format those in markdown instead of trying to auto-render it from a .bib file.