A small refactoring to create custom constructors in the models, to reduce the knowledge the controllers must have about the structure of the models.
Renamed defaults to set_defaults for clarity.
Get rid of law of demeter violation (quiz.category.name) in a couple of views
Extracted New Category and New Subject creation out into a separate class. Extracted the quiz validation related to new category and new class into a validator class.
Chnaged variable name from quiz to record to genericize it. In the future I will use this class for cheatsheets and flashcards in addition to quizzes.
For now, make quiz events have a depenedent destroy relationship with quizzes. Letting a quiz taker have access to their quiz results even after a quiz gets deleted can be an enhancement in the future.