Remove unused method preprocess(SMDataModel) in Clustering preprocessor
Clean up dependencies in PreprocessorClustering
Code formatting
Clean up imports in PreprocessorPuddis
Fix bug in Preprocessor where PseudoRatings were not reset before each run

This caused RMSE to be higher than expected because PseudoRatings were not reset after each run
Remove deprecated PreprocessorPuddis
Fix RemovePreference() in DBModel
Change DBModel.startServer to run in separate Thread
Add method DBModel.getNumPrefs()
Changes to Preprocessors

- Ensure PseudoPreferences are removed from DB after new model is passed
- Move all additions to PseudoPrefs to a single method
Add number of PseudoRatings to column output