Adds "Move To" dialog to the course settings navigation tab

Modifies the screenreader instructions group to be much simpler
just warning users to use the new dialog.  Makes the warning
appear for keyboard-only users.

closes CNVS-12799, CNVS-14733

test plan:
    1. Load up the course settings page (/courses/##/settings)
    2. Click on the gear icon in the enabled list.
    3. Click 'disable'
    4. It should now appear in the disabled list, the gear icon link
       should have changed to 'enable'
    5. Use the gear and click on move.
    6. A dialog should appear allowing you to move things within
       a list.
    7. Clicking the save button should persist changes beyond the
       current session.
    8. Repeat the above steps using a screenreader.
      a. When you tab off of the navigation tab, a warning should
         appear (and be read by the screenreader)
      b. The message should disappear when tabbing off of it.

Change-Id: Ie3d2cae23a47535d5a3995174794e0f0d853e629
Reviewed-on: https://gerrit.instructure.com/40169
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Product-Review: Cosme Salazar <cosme@instructure.com>