BREAKING: LabelSetImage::AddLayer() does not call LabelSetImage::SetActiveLayer(newLayerID) any more.
Why: 1) There where reasons where this is unwanted behavior.

2. It is not the job of AddLayer(), change maximizes cohision.
3. ActiveLayer/ActiveLabel are deprecated; thus it makes no sense to add

code complexity for them.
How to adapt: If you need to change the active layer, call SetActiveLayer
explicitly after calling AddLayer. User the return value of AddLayer.