Add feature flag to hide refactor work to theme editor
Add feature flag to hide refactor work to theme editor

closes CORE-1010

Test Plan:
  - A feature flag for "Theme Editor Refactor" is visible
    in development environments

Change-Id: I18d00b257ec632f9d496a480ade624bb564ef538
Reviewed-on: https://gerrit.instructure.com/141030
Reviewed-by: Rob Orton <7e09c9d3e96378bf549fc283fd6e1e5b7014cc33@instructure.com>
Tested-by: Jenkins
Product-Review: Robert Lamb <bf934bf7cdbebe5899399a138c0cb75c4d783999@instructure.com>
QA-Review: Robert Lamb <bf934bf7cdbebe5899399a138c0cb75c4d783999@instructure.com>

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