Make new RCE look better in RTL
Make new RCE look better in RTL

closes: CORE-2957 CORE-2956

These are just some small changes we can do to get things looking
better in RTL. We may need to do more later but this at least
keeps us on track for now

Test plan:

* turn on the “RTL even for non RTL languages” user feature flag or
  set your language to arabic
* look at the editor
* everything should be flipped and the borders and padding for the
  butttons should be the same as it was in LTR but flipped.
  (like this: https://cl.ly/683c0b29b18b)

Change-Id: Ie3a73bf0757f4180bed1faed89bde9a45c2bcaa1
Reviewed-on: https://gerrit.instructure.com/193628
Tested-by: Jenkins
Reviewed-by: Clay Diffrient <9dff2e5c98626d20d2848250c411e8009465bb87@instructure.com>
QA-Review: Clay Diffrient <9dff2e5c98626d20d2848250c411e8009465bb87@instructure.com>
Product-Review: Clay Diffrient <9dff2e5c98626d20d2848250c411e8009465bb87@instructure.com>

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