Possibly automatically unassign/hide completed (translated + accepted) tasks from the overview

Also implemented now, tasks/items are marked as closed once accepted and now shown on the default view.

Hiding is what should happen usually from pending lists.
In case of escalation and for other statistic reasons, this assignment should remain.
Thus a user can see his personal list "my completed jobs".

As long as no complex job reassignment occurs, we can easily see in history, how translators performed.

Once we have a better tracking in place and e.g. Count translated words separately per user, we can discuss about unassigning a job.