client app: canvas_quiz_statistics

This commit brings in canvas_quiz_statistics, a client app that can be
embedded in Canvas.

Closes CNVS-14781, CNVS-14846, CNVS-14847, CNVS-14850

> What's done

  - full build integration, meaning the app runs with ?optimized_js=1:
    + JavaScript "built" source gets piped into the r.js build pipeline
      like any other Canvas JS source in public/javascripts/*
    + SCSS sources get picked up by the sass-compiler like Canvas style
      sources and they get compiled from the grounds-up
    + I18n: phrases are extracted properly, with default values and
      options, by our i18n rake tasks
    - new rake task js:build_client_apps that builds client apps and
      injects them as input to the rest of the JS build process
  - support for using Canvas JS packages, like d3, jQuery, and Backbone
  - support for using Canvas SASS variables & helpers
  - super i18n support: use raw I18n.t() calls like you are in Canvas,
    with development-time interpolation, as well as super new
    Handlebars-like block-style translations in React, perfect for very
    long phrases (mini-articles)

> Docs and References

The code was originally developed in its own github repository. While I
won't be pushing code to that repo anymore, the Wiki will still house
the docs until we find a better place.

  - Repo: https://github.com/amireh/canvas_quiz_statistics
  - Development guide: http://bit.ly/1sNOhER
  - Integration guide: http://bit.ly/1m9kA9V

> TESTING

  - login as a teacher
  - go to /courses/:course_id/quizzes/:quiz_id/statistics_cqs
    + make sure you see something that looks like the Ember stats
    + click one of those little "?" help icons, you get a dialog:
      - verify the contents within the dialog are actual English text,
        not code gibberish
      - there's also a link at the end of that dialog, click it and
        verify it takes you to an Instructure help article
  - build the assets: `bundle exec rake canvas:compile_assets` then:
    + add ?optimized_js=1 to the URL and reload the page:
      - verify the app still works

Change-Id: Ic474650dfb06a1c22869ed9680dd04d1ca0f651d
Reviewed-on: https://gerrit.instructure.com/39105
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Hannah Bottalla <hannah@instructure.com>
Reviewed-by: Adam Ard <aard@instructure.com>
QA-Review: Trevor deHaan <tdehaan@instructure.com>
Product-Review: Ahmad Amireh <ahmad@instructure.com>