Accessibility: Moved the right sidebar to after the main content in the DOM

Fixes CNVS-6699

Test Plan:
- Click through a few pages with and without a breadcrumb nav

Change-Id: Ib1c1e03ce6b63623b0e3ba778ac78ce4bd1b60cf
Reviewed-on: https://gerrit.instructure.com/28534
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Amber Taniuchi <amber@instructure.com>
Reviewed-by: Ryan Florence <ryanf@instructure.com>
Product-Review: Ryan Florence <ryanf@instructure.com>