FastFM wrapper

[tlikhomanenko]

Add wrapper for the factorization machines

[arogozhnikov]

Results of FastFM digging at this moment:

• FastFM is pip-installable on mac os and ubuntu (which is very good point)
• at the same time, doesn't completely follow sklearn interface (need also to check cloning and dumping - I haven't done this yet), this is resolvable
• I've run some tests and FastFM lost the competition to original LibFM.
  • MCMC were tested, but I am quite sure it is useless (one can't even save the formula in this case).
  • I hope that ALS implementation is better (and ALS is the only useful in practice), but this needs to be checked.