get rid of ITimedDataSet, fix indexing bug in InteractionReader
ExternalItemRecommender and ExternalRatingPredictor now use the Interactions
do not use RatingData in ExternalRatingPredictorTest
rm class RatingData
rm class Ratings
rm (I)DataSet, IRatings, RatingType, IndexedMemoryReader, MemoryInteractions
source tree: move new data stuff into the normal data folder