Update all Dutch articles with the new style and other adjustments

Dutch RouteNet articles now use the common style
Change file encoding to Unicode UTF-8
Convert special characters to their UTF-8 version (i.e. é, ï, ö, ..)
Make assignments stand out more
Ensure that all figures are centered
Update screenshots of public database
Update links to public database
Update some image names
HiSparc -> HiSPARC
Rewrap some paragraphs
Fix name of 'De Hemel' article
Regenerate all pdfs