Makes it so links are clickable in the course menu

Makes the selector for the link following cancel logic a bit
more specific.  Adds tests to make sure that the menu does not
go to the courses index page and so that clicking a link for a
course does indeed take you to the course.

fixes CNVS-15538

Test Plan:
  - Open up Canvas and click on the "Courses" global nav item
  - It should open the menu and that's it.
  - Click a link to a course
  - The link should take you there.

Change-Id: Icd7e4684aef1b45c4135713e70fba495d8d2b2e5
Reviewed-on: https://gerrit.instructure.com/41159
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>
Reviewed-by: Ryan Shaw <ryan@instructure.com>
Product-Review: Ryan Shaw <ryan@instructure.com>