Add toolbar button group separators to floating toolbars
Add toolbar button group separators to floating toolbars

closes COREFE-192

test plan:
  - open a page with the rce
  - with the browser narrow enough so that the last 2 toolbar button
    groups are hidden, click the kabob button
  > expect the grey line between the toolbar button groups in the
    overflow toolbar that pops up
  - add a table to the RCE, and put the cursor w/in it
  > expect the popup table context toolbar to have the grey line
    between the button groups

Change-Id: I825f421ffc9e33fc4c281d4704dc2394dbfcf57e
Reviewed-on: https://gerrit.instructure.com/203314
Tested-by: Jenkins
Reviewed-by: Ryan Shaw <ea3cd978650417470535f3a4725b6b5042a6ab59@instructure.com>
QA-Review: Ryan Shaw <ea3cd978650417470535f3a4725b6b5042a6ab59@instructure.com>
Product-Review: Ryan Shaw <ea3cd978650417470535f3a4725b6b5042a6ab59@instructure.com>

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