convert font-size within feature-flags from px to rem
convert font-size within feature-flags from px to rem

Fixes: CNVS-26383

test plan:
- as a user navigate to the account settings
- scroll to the bottom where the "Feature Options" appear
- in chrome preferences "advanced settings" select
  font size large or very large
- the details should now enlarge respectively

Change-Id: Ia7dcf46a04d3e1eac75cae5e81ba145182084628
notes: http://screencast.com/t/wWkeVsC90y
Reviewed-on: https://gerrit.instructure.com/70120
Reviewed-by: Colleen Palmer <387ba1943871e60965e6b44638a2f2e1ab9b8469@instructure.com>
Product-Review: Colleen Palmer <387ba1943871e60965e6b44638a2f2e1ab9b8469@instructure.com>
Tested-by: Jenkins
QA-Review: Myller de Araujo <e5c7c5e1b7f2ce5e9870cc98ec52b20b3006cb48@instructure.com>

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