Add ReactiveCollectionViewSource and ReactiveCollectionViewCell.
New internal class CommonReactiveSource.
Merge pull request #1 from meteficha/ReactiveCollectionView

New internal class CommonReactiveSource.
Safer disposing.
Formatting only.
Remove finalizer in CommonReactiveSource.

Also, seal class and remove virtual Dispose method.
Merge remote-tracking branch 'origin/pr/397'