Support gloomhaven scenario tree

[asphaltbuffet]

It would be great if saving also created a notebook page with data in the format to use with Gloomhaven Scenario Tree (https://dmungin.github.io/gloomhaven-scenario-tree-ng/).

[Sebaestschjin]

Thanks for the link, this looks cool. I'll look it into how the data is required, but I guess that should be doable.