public void Teardown()
{
_surface.MouseLeftButtonDown -= OnSurfaceMouseLeftButtonDown;
_surface.MouseMove -= OnSurfaceMouseMove;
_surface.MouseLeftButtonUp -= OnSurfaceMouseLeftButtonUp;
Workflow.ActivityAdded -= OnActivityAdded;
Workflow.ReferenceAdded -= OnLinkAdded;
Workflow.ReferenceAdded -= OnLinkAdded;
Workflow.ReferenceRemoved -= OnLinkRemoved;
}