1) In Krita we have a "weird" system, where KisCanvas2 switches shape
   managers depending the currently activated shape layer/selection.
   I call it "weird" not because it is bad, but because Flake system
   was not designed for that. Quite a lot of dockers and objects
   make connections to a KoSelection, and keep these connections
   throughout the entire run of Krita. That is wrong behavior in Krita.

2) To solve the issue I created a special proxy object:

   KoCanvasBase::selectedShapesProxy()

   which has the same selection signals provided by KoSelection and
   KoShapeManager, but that is guaranteed to be persistent throughout
   the entire life of KoCanvasBase.