Canvas UI Component Update - Accordion

Fixes: CNVS-15535

Creates a new stylesheet in /components with our
updated accordion styles from the brand styleguide.

Test plan:
- Open the /styleguide from the main Canvas URL.
- Accordion should be the first item listed.
- Check the implementation against the following
  screenshot from the styleguide:
  http://cl.ly/image/0Y3I0X3l1V1g/accordion.png
- Go to Assignments, Pages, Quizzes and Announcements
  and make sure the mini accordion is looking right
  and the pages continue to function properly.

Note for code review: jQueryUI inserts its own classes,
so consistent with Tabs, I did not create .ic- prefixed
classes.

Change-Id: I22eb57ffb57c58aa69cc728d60e5bd225dbf6d02
Reviewed-on: https://gerrit.instructure.com/44090
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Colleen Palmer <colleen@instructure.com>
Product-Review: Colleen Palmer <colleen@instructure.com>
QA-Review: Nathan Rogowski <nathan@instructure.com>