Game Best/Worst Refactor

Refactored game best/worst into proper method on model instead of the logic residing in the controller.

Cleaned up the fixture yml classes by using [fixture associations](http://api.rubyonrails.org/v3.2.13/classes/ActiveRecord/Fixtures.html#label-Label+references+for+associations+%28belongs_to%2C+has_one%2C+has_many%29). Built out the fixtures with a few sample game sessions to allow for proper tests.