Add command: "Fold to tasks due next"

[shalecraig]

I usually try to work on the next task that's due.

This is easy to do when I have some overdue/upcoming tasks -- just use Tasks: Fold to due tasks, and select the most-overdue tasks first.

However, this isn't as easy when I'm ahead of myself (I try to stay ahead of my due dates). Because of this, I try to grab things that I don't need to do until then.

Implementation/Decisions.

• Shamelessly, I copy-pasted most of the due_soon implementation, collecting "interesting" (aka parsed) (due timestamp, line) tuples, and sorted/took the first 10 at the end.
• There's a TODO in there about setting up a sample/default value -- I'm not sure if there's a Default settings file I need to add the new settings to.
• Most of the settings for the next_tasks fallback to the due_soon values instead of having their own defaults.

[vovkkk]

Why not make it a default behaviour?
E.g. if there are no overdue and soon, but there are some next, we could ask user should it fold to next or not (with ok_cancel_dialog).
And there might be a setting for dialogue: ask, use next without asking, no asking and no folding.

[shalecraig]

Hmm, this is some good feedback.

Let me see what I can come up with -- it might not be immediate, but in a few days.