Support for KO 3.0 array change subscription 

Maybe there is a better way to get this in, but this is what I use atm to give me the hints when doing .subscribe.

From one of my use cases in a generic class.

```
        childs: KnockoutObservableArray<T> = ko.observableArray([]);
        this.childs.subscribe((changes: KnockoutSubscribtionArrayChangeEvent<T>[]) => {
            changes.forEach(change => {
                if (change.status === 'added') {
                    change.value.layout = this;                        
                } else if (change.status === 'removed') {
                   delete change.value.layout;
                }
            });
        }, null, "arrayChange");
```