private void AddProductionOffItem(object o)
 {
     ProductionOff.Add(new Item {
         Date = DateTime.Now, Duration = new TimeSpan(1, 0, 0), GroupName = "Période d'arrêt"
     });
     UpdateTimeline();
 }
 private void DeleteProductionOffItem(object o)
 {
     if (ProductionOff.Count != 0 && ProductionOffSelectedItem != null)
     {
         ProductionOff.Remove(ProductionOffSelectedItem);
     }
     UpdateTimeline();
 }