increase 10px font size throughout gradebook to 12px min
increase 10px font size throughout gradebook to 12px min

Refs: CNVS-26581

test plan:
- as a teacher using the old or new ui
- navigate to a course that has users that have submitted assignments
  that have been graded so you can view gradebook
- click the grades sub-nav link
- from the gradebook view the following have been updated
  - ko accessibility warning: http://screencast.com/t/2q5qqEqwfes
  - student section: http://screencast.com/t/sNQcjOecb4
  - secondary identifier: http://screencast.com/t/9BwHyVcbJI2C
  - slick header column: http://screencast.com/t/rp1InVw4Qmx3
  - assignment-points-possible: http://screencast.com/t/FAYK4WHMLO2
  - letter-grade-points: http://screencast.com/t/ZNDLWnbS

Change-Id: I2b19daf410bd3e10dc74ee999f9e8b1439f11262
Reviewed-on: https://gerrit.instructure.com/72841
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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