added AI logic to play more than 1 card if possible

added IsSelected property to card and binding in ListBox so that also AI can select cards
fixed MEF import problem that AI implementations for both players have same shared instance
fixed problem that games are not reinitialized when starting them again (now new instances are created from ExportFactory)

added workaround for task problem
changed CPU task to use continuation for ending turn to hopefully fix the ListCollectionView problems