Allow different voting URL for normal and quiz questions
Die resource routing

It's a mess that works only for typical CRUD.
Create abstract BaseQuestionsController
Extract common stuff into BaseQuestionsController
Show link to next question in quizzes

Also:
* change quiz routes to use question number instead of a slug,
* add pry to Gemfile for easier debugging
Fix tests
Make the first question number 1 in quiz URL
Be explicit where we want next_question_path
Move the next button outside of application layout
Rename next_question_path to next_path

Can be used for Done button too.
Show link to quiz results after the last question

Also fix constraints in some routes.
Add quiz results page