Add a bibtex citation file for each publication

[SvenLieber]

With the newest Wowchemy version I started to use (f468f84) there is the possibility to add a bibtex file to each publication. Visitors can click on a cite button to get the bibtex description of the publication. I should apply this to all available publications.

[SvenLieber]

Such a file can be generated with a script based on the work-in-progress central research-output.bib file (#22), similar to a script that computes KPIs (#23)