mastery gradebook: visibility filters never apply to average row

the visibility filters were only being applied when changing the
average calculation type or when switching sections.

fixes CNVS-10495

test plan:
 - have students with outcome results that produce a variety of
   class averages.
 - toggle visibility off for one or more of mastery/near
   mastery/remedial. all averages should still be visible and
   their value should not change.
 - with some visibility turned off, change the average
   calculation type. all averages should still be visible and
   updated to reflect the selected average type.
 - with some visibility turned off, change the selected section.
   all averages should still be visible and should be
   recalculated for the selected section.

Change-Id: I8f24023aad0a5beaf52bdf993e019316394a2666
Reviewed-on: https://gerrit.instructure.com/28903
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Braden Anderson <banderson@instructure.com>
QA-Review: Matt Fairbourn <mfairbourn@instructure.com>
Product-Review: Jon Willesen <jonw@instructure.com>