frd *always* use fetch polyfill for edge <17
frd *always* use fetch polyfill for edge <17

Refs: CORE-3225

This also runs the polyfill before loading new relic so that if anything
uses “window.fetchIgnoredByNewRelic” it is the polyfilled version

Test plan:
* in edge 42, load the assignment show page
* you should not get an error in the console like:
HTTP401: DENIED - The requested resource requires user authentication.
(Fetch)GET - https://<canvas>/api/v1/courses/11/lti_apps
/launch_definitions?placements%5B%5D=assignment_edit
* you should also not get an error like that for the
  https://<canvas>/api/v1/conversations/unread_count request

Change-Id: I65ab0a096d6fe4643975623d68dc88ac520e5559
Reviewed-on: https://gerrit.instructure.com/204432
Tested-by: Jenkins
QA-Review: Tucker Mcknight <4b51b98c1d84aa97854d216bd061ce5d3eda8a28@instructure.com>
Reviewed-by: Weston Dransfield <e9203059795dc94e28a8831c65eb7869e818825e@instructure.com>
Product-Review: Weston Dransfield <e9203059795dc94e28a8831c65eb7869e818825e@instructure.com>

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