adding to the Score module to calculate expected values of beers

1) unrated_beers method returns an array of unrated beers of current user compared to another user
2) expected_value_of_unrated_beers method returns a hash of the expected values of unrated beers of current user compared to another user
3) all_expected_values_of_unrated_beers method returns a hash of all expected values of unrated beers by all other users