Once I built the basic widget, it turned out to be rather easy to replicate
it once per scheduled activity and wire it all up to a fully working UI.
This does abuse yesod's form handling a bit, but I think it's ok.
And it would be nice to have it all ajax-y, so that saving one modified
form won't lose any modifications to other forms. But for now, a nice
simple 115 line of code implementation is a win.
This late night hack session commit was sponsored by Andrea Rota.
