Allow for single event for all properties with [Notify] attribute

[Hendrik-Mueller-Overzone]

I use the NotifyAttribute for all kind of UI work, where I want a control to update, when UI-relevant data of the object has changed. This works great for a few proeprties with the current setups but doesn't scale well, when the number of properties with the NotifyAttribute increases, as each one requires a new subscription and desubscription of the event handler.

It would be greate if there was one event generated, that is triggered when any of the properties with the NotifyAttribute changes.

[Cat-Lips]

[Notify] properties on a Resource class already trigger the Changed signal, but I think it could be useful to add one for non-resource classes. Good idea :)