Integrate surprise for recommender systems/collaborative filtering

[kveerama]

Surprise provides a variety of solutions for recommender systems. It has SVD, SVD++, NMF, Slope One, k-NN, Centered k-NN, k-NN Baseline, Co-Clustering, and Random. It is pretty close to scikit-learn API so perhaps we only need JSONs to add them as primitives. https://github.com/NicolasHug/Surprise