Add detail to list

[b-per]

Hi @pomdtr !

I was checking if it was still possible to add a detail to a list item, like described here, but I don't see it in the JSON schemas anymore.

Was this removed in the latest refactor? And would you think of adding it back?

[pomdtr]

There is two issues with detail attached to list items:

1: highlighting issue (see muesli/reflow#52)
2: I still need to figure out a good api for dynamic update

I plan to tackle this after V1