EXP-336.  Add cosine, pearson similarity to modeling.

Also update Jaccard distance calculation to use the Scalding Matrix
library.

Cosine similarity and Pearson similarity match LensKit implementations.

Cheers to Amit for recommending the Scalding Matrix library and for
pointing Renuka and me to a paper that shows how Mahout implements
item-item similarity methods in a modular manner!!!!

review: https://review.kiji.org/r/1432
issue: https://jira.kiji.org/EXP-336