Version 1 of #3396

I can take this opportunity to replace manual markdown with a proper text editor. Then there’s no need for autopaired brackets.

The editor will need to support:

• Automatic links to ideas like #123
• Links to @mentions like @dennis-hackethal
• Safe link formatting
• Disabling of turbo links
• Namespaced footnotes
• Custom blockquote format
• Protection against XSS