Drag should be allowed when sorted

[ITDancer13]

At the moment the following statement prevents that items are dragged from a TreeDataGrid as soon as the source is stored.

var allowedEffects = AutoDragDropRows && !_source.IsSorted ? DragDropEffects.Move : DragDropEffects.None;

I can clearly see that dropping it would be a problem as it cannot be correctly determined where to move it to. However, dragging it to other parts of the user interface should not be a problem.

Maybe it also would be a opportunity to split AutoDragDropRows in the same step.