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.
The student assignment would not be blank if the instructor is also a student

On Jun 27, 2014, at 8:55 PM, Lakshmi <notifications@github.com> wrote:

> In app/views/assignments/show.html.erb:
> 
> > @@ -82,11 +82,15 @@
> >    <% end %>
> >  <% end %>
> >  
> > -<%= section "Exercises", {:classes => 'no_bar exercises'} do %>
> > +<%= section "Exercises", {:classes => 'no_bar exercises', :collapsible => authority?, :collapsed => authority?} do %>
> >  
> >    <% if @student_assignment.blank? %>
> Hmm... if the instructor did sign up, would the student assignment be blank? (BTW, this is not new code.)
> 
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