Make RuboCop output in default rake task more useful

It is helpful to see what's wrong as well as the files which have RuboCop
violations.
Issue #11: Allow basic reordering of a quiz.

This allows us to use a couple of reordering vectors to "shuffle" a Quiz and
generate a QuizVariant:

* answer_reordering_vectors - an Array of ReorderingVectors which map
  to the Quiz's Questions, and specify how each Question's Answers are
  to be reordered.
* question_reordering_vector - a ReorderingVector which specifies how a Quiz's
  questions are to be reordered.

Effectively Quiz + answer_reordering_vectors + question_reordering_vector gives
us a predictable QuizVariant which can be rendered into a question sheet and
answer sheet.
Merge pull request #13 from mikestok/issue-11

Issue 11