The App calculates Elo

* When a match winner is submitted, the player's elo is upated
* Create CalculateElo class
* Create EloUpdater class
before I just had it return `t_ratings` at the end of `calculate_transformed_ratings` but I felt like that was bad. Would it be preferable to just have a `calculate` method that calls `calcualte_transformed_ratings` and then returns `t_ratings`?