course catalog

test plan:
  * open a course's settings page
  * enable listing the course in the public index but not
      making the course content public
  * open the course home page as an unregistered user
  * verify that only the course's title and description are accessible

  * open root account feature flags page
  * enable Course Catalog

  * open your "My Courses" page
  * verify that the right pane includes a "Browse more courses" link
  * click the link
  * verify that you can browse courses allowed in the public index

  * log out
  * verify that the homepage includes a "Browse courses" link

Change-Id: I44f96396859283d76bfe527672612ff71ca4ae67
Reviewed-on: https://gerrit.instructure.com/24682
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Braden Anderson <braden@instructure.com>
QA-Review: Trevor deHaan <tdehaan@instructure.com>
Reviewed-by: Jon Jensen <jon@instructure.com>