Add "identifier" & "datePublished" to the codebook and update the citation (when all info is available)

[elinalutz]

identifier & datePublished: fill in the info in lines 72-73 in the R Markdown script
citation: fill in publication year (currently "in press"), journal, volume, issue, page range, doi in line 32 in the R Markdown script

remark: the fields "measurementTechnique", "funder", and "keywords" are prepared in lines 69-71, but the formatting in the html-file is not very nice (see screenshot below, keywords not yet filled in); if you find a way to make this more appealing, feel free to comment these lines back in