When sorting by due-date, use the closest date of all children

[Izidor Matušov]

I sort my tasks by due date. Many times I have this situation:

task_without_duedate
-> task_with_duedate_tomorrow

Because the parent has no due date, it is in the middle of other tasks with no due date. Although it requires my attention (it's child must be done tomorrow!), it is not at the top.

I think tasks should "inherit" due-date from they children (and their children) and set to the closest due date. This due date do not have to be displayed anywhere, just used for sorting.