investigate integration with Mermaid for graphs

[bjornregnell]

Perhaps use this for graphs:

• https://mermaid.js.org
• https://github.blog/developer-skills/github/include-diagrams-markdown-files-mermaid/

It is in js so maybe we first need to ditch reqT in Swing in favour of ScalaJS on npm perhaps Electron or something ...

• Should this replace graphviz?
• Should we use pandoc? https://bagelquant.com/pandoc-with-mermaid/

[bjornregnell]

see also https://sake92.github.io/flatmark/ for inspiration on how to create mermaid diagrams from markdown