Feature Request: Method to not include scene in numbering

[chrisgrieser]

In some cases, I do want to include a scene in the longform project, but do not want to include it in the chapter count. Take for example this one: Here, the two appendix chapters and the metadata chapter should not get the numbering.

Best I could do via CSS is to make those chapters gray, but removing the numbering from "Metadata" would have the annoying side effect that the introduction would start at 2…