Pass Property to ChangeEvent

[CodeRhymesLife]

Will make event handling much cleaner

[CodeRhymesLife]

I still want to do this, but, with the way things are now, this change would turn Property into Property<T, PT>, where T is the value type and PT is the property type (e.g. GameObjectProperty). The reason we need PT would be to have the right type passed to the onchange handler in the Property base class. I like Property the way it is because it can be used by other, non-GameObject related objects. It's a nice thing to have.

But it would also be much easier to handle events if the property was passed to them. Keeping this open for the next version.