lml/ost#345: Add questions with links to exercises section.

- Add `family` scope and method to the assignment model.
- Add `_questions` partial to show the exercise questions.
- Add `show_url` param and ability to the `_question` partial.
- Add `authority?` view helper function.
- Use `authority?` view helper function.
- Fix copyrights.

TODO:

- The styles for questions are a little weird.  Leaving things
  as is to wait for the UX review.
What you probably don't want to hear is that helper methods are globally available across all views.  So this `authority?` method could be called from some other random view -- no scoping / namespacing :-(  Of course this means that a name like `authority?` is too generic.  

In this case, since this method is only used from one view file (see my other comment about the use in the controller), what you should do is just define

    authority = @assignment.cohort.klass.is_educator?(present_user) ||
                Researcher.is_one?(present_user) ||
                present_user.is_administrator?

and use that variable where you currently use `authority?`

http://nicksda.apotomo.de/2011/10/rails-misapprehensions-helpers-are-shit/