CommonReactiveSource allows section info list to be updated.

Note that now we require at least IReadOnlyList instead of
just IEnumerable.  I argue that this is the morally correct
thing to do since it allows us to ditch .ToList().
Reactive{Collection,Table}ViewSource now are IReactiveNotifyPropertyChanged.

Uses copy-paste from ReactiveNSView.
Stronger-typed CommonReactiveSource.
New Data property for Reactive{Collection,Table}ViewSource.
CommonReactiveSource now reacts to section changes.
Fix a couple of boring bugs.
Oh, snap!