add keyboard shortcut help to syllabus

fixes CNVS-16721
fixes CNVS-15961

This adds the blue help icon next to HTML Editor text.

Test Plan
As a user that can edit the syllabus
When you go the the syllabux page
And you click on the 'edit' button
Then you should see the tinymce editor
And there should be a blue help icon next to "HTML Editor"
And clicking on it should show the keyboard shortcuts help menu

Change-Id: I3e629506b9c331a7d4a3640d0bceb4071506f21f
Reviewed-on: https://gerrit.instructure.com/43971
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Dan Minkevitch <dan@instructure.com>
Product-Review: Cosme Salazar <cosme@instructure.com>
QA-Review: Jahnavi Yetukuri <jyetukuri@instructure.com>