add tinymce help menu when creating or editing wiki pages

fixes CNVS-16720

The help icon should now appear next to the toggle the tinymce
editor/html button.

Test Plan
- Test this on both the new wiki page and edit wiki page
As a user that can creating or editing a wiki page
When I'm on the new wiki page, or edit wiki page
I should see a help icon next to "HTML Editor" text (blue circle with
"i" in it)
Clicking the help icon should open the shortcut help dialog

Change-Id: Ic988af3bda092d053e683edc0c0b1ef53cac2fd4
Reviewed-on: https://gerrit.instructure.com/43963
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>