Feature Request: Do not Group Completed tasks by list or bucket and Add completion date to tasks

By default, when selecting Completed, we see all completed tasks per list or per bucket. 
Its not easy to see all completed tasks of last week. When you would remove this grouping, the overview is already better.

Next to that, it would be valuable to have a completion date when completing a task. And then being able to sort on completion date, instead of due date or added to my day or creation date.