Add support for TracLinks in Mermaid flow chart diagrams
|Reported by:||cboos||Owned by:||tkob-trac|
It seems this is the only type of diagram which supports adding links, in mermaid.
The patch will be on top of the patch from #13039.
In this patch, I also add a link to mermaid.css. You can obtain it from https://github.com/knsv/mermaid/raw/master/dist/mermaid.css and copy it below tracmermaid/htdocs.