Add Factorization Machines to ML.NET

[sfilipi]

Add the train a field-aware factorization machine algorithm to ML.NET as described in the following papers:
[1] http://jmlr.org/papers/volume12/duchi11a/duchi11a.pdf
[2] http://www.csie.ntu.edu.tw/~cjlin/papers/ffm.pdf
[3] https://github.com/wschin/fast-ffm