The App calculates Elo

* When a match winner is submitted, the player's elo is upated
* Create CalculateElo class
* Create EloUpdater class
I would also mention that your `CalculateElo` class is a bit to coupled to your `TRatingCalculator`. It knows a bit to much about how the `TRatingCalculator` works.

`CalculateElo` should not know that you need to call `calculate_transformed_ratings` before being able to call `t_ratings`.