Handling of incompleted tasks at the end of the day

[Konzertheld]

At the end of the day (see also #15), move incompleted tasks after the following principle:

• Look for the next day that has free space for this task.
• If the task does not have a deadline, move it there and tag it as overdue.
• If the task has a deadline that has expired, mark it as expired and see Handling of appointments (imported from Google) / Expired tasks #25
• It the task does have an unexpired deadline and the next day with enough free space is within the deadline, move the task to that day and do not mark it as overdue.
• If the task has an unexpired deadline and the next day with enough free space is not within the deadline, search for the next day that could have free space if a single other task that does not have a deadline was moved.
• If that day is within the deadline, move the task there and move the other task according to the rules above except that it is not marked as overdue.
• If that day is not within the deadline, ignore the search result. Move the task to the next day. If the schedule is so full, the user has to live with the fact that incompleted tasks just pile up the next day.

[Konzertheld]

Further optimization: When searching for a day that has enough free space within a deadline if tasks are moved, chose the day where the least tasks need to be moved.