Fixes problems with BaseEstimator class deprecated import _set_param and Implements a hybrid method combining Collaborative Filtering and Global Baseline estimates to deal with cold start

[gabrielspmoreira]

• Fixes problems with BaseEstimator class deprecated import (scikits.learn.base) (Issue Bad scikit-learn import in crab/base.py #90 ) and _set_param renamed method (Issue No Attribute named _set_params #94 ) making it compatible to the last stable scikit-learn version '0.15.2'
• Implemented a hybrid method to combine Collaborative Filtering with Global Baseline estimates (based on users and items average preference), to deal with users and items cold start, inspired on Implementing Collaborative Filtering class from Coursera Mining Massive Datasets course.