Add yoochoose utility

[mokarakaya]

In recommender_datasets v0.2.0, I see yoochoose dataset hdf5 files.
I guess this is the dataset used in RecSys 15 Challenge.

Is the utility class of the dataset already available to use in another branch?
If not, do you mind if I add it in a new MR?

I don't know if you're planning a more comprehensive MR with all changes in the new version of recommender_datasets.