Relocate global nav Trays
Relocate global nav Trays

The global nav trays were mounted in <div id="main">, so the Tray
component could not aria-hide all of <div id="application">, or it would
hide itself. By moving the Trays' mount node outside of the application
itself, we can trap the screenreader's navigation entirely.

fixes ADMIN-1005

test plan:
  - with a screenreader active, navigate to the Account
    button in global nav
  - using the screenreader's reading navigation commands
    (in VO it's ctrl-opt-right and left arrow), attempt
    to read out of the Tray
  > expect that you cannot.

Change-Id: I8cc982fb093c195f50b215a64184cb74981fa125
Reviewed-on: https://gerrit.instructure.com/150957
Tested-by: Jenkins
Reviewed-by: Jon Willesen <0321efbc0acf6204eb6035acb1d418838b450d08@instructure.com>
Reviewed-by: Carl Kibler <7c2b40129dd885a147d5b2dda56dda016b9a8f57@instructure.com>
Product-Review: Dan Sasaki <ae19fabf7fe19dff310008c9b6a4d2ec84d311d8@instructure.com>
QA-Review: Dan Sasaki <ae19fabf7fe19dff310008c9b6a4d2ec84d311d8@instructure.com>

djbender/canvas-lms,djbender/canvas-lms,instructure/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms