Better manage plannings assignments for inactive projects

When a project is marked as "Complete" and/or archived or deleted it disappear from the planner, and the capacity blocked before is free again. This leads to a distortion in a target-actual comparison of the working times of the past months. It would be better to stop the Planner entry on the day of completion (archiving) and to continue to display the assignment in the past (until the day on which the project was marked as "Complete").