RCE's pretty html editor arrow keys are working
RCE's pretty html editor arrow keys are working

Pretty html editor now supports arrow keys navigation
and Ctrl-Key commands.

fixes MAT-97

flag=none

test plan:
- Navigate to a RCE instance
- Switch to pretty html view
- Type some text
- Move the text caret with the arrow keys
- Select all text with Ctrl/Cmd + A

Change-Id: I196e864fd2d9c2b65356fba75637849ef732f4ed
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/264402
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Ed Schiebel <0ca8a83847a5889cf05cb219c0ab09f6b646243b@instructure.com>
QA-Review: Ed Schiebel <0ca8a83847a5889cf05cb219c0ab09f6b646243b@instructure.com>
Product-Review: Juan Chavez <8fc9c8a746010dcf1babfbe57a3b7ae7798e6eeb@instructure.com>

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