Some more enhancements to Prism based syntax highlighting

Right now the bundled Prism file to support syntax highlighting (cf. #490) supports these: markup (covering html, xml, svg, mathml, ssml, atom, rss), CSS, C-like, JavaScript (js), C, C++ (cpp), Bash (sh, shell), Diff, Git, Go, JSON (webmanifest), Makefile, Perl, Python (py), Ruby (rb), and YAML (yml).

The following plugins are also bundled Autoloader and File Highlight.

I think we might be able to strip the supported languages significantly to only those that are used in the repository. This would reduce the bundle download size.

A few other things to check:

• It seems the Prism header from the artifact downloaded from the website has been removed. I think we can retain that.
• We might need to check if it is possible to achieve the same syntax highlight in the e-mail version of the newsletter @mjaix

cc @Amrit-raj50

Untersuche das gebündelte Prism-Artefakt und ermittle, welche der unterstützten Sprachen tatsächlich im Repository verwendet werden. Prüfe, ob der Prism-Header beibehalten werden kann und ob eine gleichwertige Syntaxhervorhebung in der E-Mail-Version des Newsletters funktioniert; abgeschlossen ist die Aufgabe, wenn das Bundle kleiner ist, ohne die erforderliche Hervorhebung oder den Header zu verlieren.