Add a due date to recurring tasks

Right now, recurring tasks do not have a due date.

This is incorrect, since recurring tasks actually have multiple due dates, the most important of which is the earliest one that isn't marked done.

Because Morgen ignores the upcoming date on recurring tasks, it fails to prioritize and visualize these recurring tasks effectively. This leads to missing important task deadlines, which is a serious flaw.

Examples:

1. I have a quarterly "File state quarterly taxes" task. It is scheduled for the first business day of every quarter. If I do not check it off, Morgen blithely ignores it and my state taxes are late.

2. I have a bi-weekly "Send invoices" task. It is scheduled every two weeks, on a Monday. Invoices need to go out in a timely manner – but, since this is recurring, Morgen effectively ignores it.

In both cases, Morgen does not "see" missed (unchecked) tasks after they are due.

In fact, such tasks are late, and should be prioritized.

Feature request

1. Have Morgen treat the earliest unchecked recurring task as the "next" task, and prioritize it accordingly. This way, if either of the above tasks are not checked, the following day Morgen will treat them as important, remind me, and try to reschedule just those missed tasks.