Adding the output prediction values for all hte items as part of evaluation for the top N recommender.
Adding the simple cached item scorer. (ticket #453)
Adding the combine function in the sparse vector. (#467)
Update the simple cache scorer to follow the conventional flow and minor renaming on write recommendations function.
Rename SparseVector.combine to combineWith (#487)
Use scores.immutable in cached scorer
Merge branch 'feature/scahng8000-topN-recommender' (PR #454)

- Closes #467
- Closes #453