Add CollectionView stub
Add initial implementation of CollectionView and tests
Call Refresh() after setting filter
Add NewItemPlaceholder property to CollectionView
Add CultureInfoIetfLanguageTagConverter stub
Add CollectionViewGroup stub
Add IValueConverter interface
Add ListCollectionView stub
Add PropertyGroupDescription stub
Merge pull request #6 from antoniusriha/collectionView

Add initial implementation of CollectionView and related types