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.
I hate GH's squashing of code review comments :-)  Per my other comment, you don't need to duplicate code (and you should not).  Just set an `@authority` variable in the controller method, set `@include_mathjax = @authority` in that controller method, then use `@authority` in the view.  Alternatively, you could actually define `@authority` in the view if you wanted (with or without the `@`) and move `@include_mathjax = @authority` to the view.