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.
You can still set a member variable in the controller, and it will be accessible to the view, e.g. in the controller:

    @authority = blah
    @include_mathjax = @authority

then use `@authority` in the view

On Jun 27, 2014, at 8:54 PM, Lakshmi <notifications@github.com> wrote:

> In app/helpers/assignments_helper.rb:
> 
> >  module AssignmentsHelper
> > +  extend Memoist
> > +  def authority?
> Yikes. Okay, will resort to using a variable. I wanted to reuse code between controllers and views - out of luck I guess.
> 
> —
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