Make WhenAny use INotifyPropertyChanged instead of IReactiveNotifyPropertyChanged

[neurotwit]

WhenAny requres IReactiveNotifyPropertyChanged instead of INotifyPropertyChanged like ObservableForProperty. This is annoying b/c I don't want my model classes to depend on ReactiveUI but I want the behavior of WhenAny to sync my ViewModel with the model. There doesn't appear to be a need to use IReactiveNotifyPropertyChanged instead of INotifyPropertyChanged.

[anaisbetts]

Hmmm, I guess I could do that, though there is a perf hit. I'll look into it, thanks!