AddRange and RemoveRange methods of Bindable...

Collection<T> will now have NotifyCollectionChangedAction value of Add
and Remove rather than Reset.

Since I didn't see a contributions guideline I wasn't sure if you wanted an issue opened or just put up a pull request to get the discussion going. So here it is!

`NotifyCollectionChangedEventArgs.Reset` seems a little heavy handed for `AddRange` and `RemoveRange`. Forcing any listener to clear their own collection (if they have one, this seems to be a common use) and repopulating. So I've opted for changing them to `Add`/`Remove`.
Supplying an index of `-1` to each to indicate that they are not index dependent operations.
[MSDN link for used constructor](http://msdn.microsoft.com/en-us/library/ms653208%28v=vs.100%29.aspx)