use dark gray text for module items in student view

test plan:  with draft state enabled,
 - view modules page as a student
   - module items should be dark gray
 - view modules page as a teacher
   - published module items should be green
   - unpublished module items should be gray (lighter than the
     color students see)

fixes CNVS-10976

Change-Id: If621d4cfd917d5a878bf2149da5f9c5f665c0c58
Reviewed-on: https://gerrit.instructure.com/30949
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Bracken Mosbacker <bracken@instructure.com>
Product-Review: Bracken Mosbacker <bracken@instructure.com>
QA-Review: Matt Fairbourn <mfairbourn@instructure.com>