Move view logic from Event into Decorator

* Move view logic from event to EventDecorator
* Decorate all EventsController methods and Mailer methods
* Move invitees_for_json into the job which uses is
* Add test for Event#to_param
* Use send for factory generation
* Move Event validation methods to private methods

Minor:
* Sort Event callbacks by lifecycle phase
* Sort private methods by order of use
* Remove redundant test for generating uuid
* Sort EventDecorator specs to match class