round scores in student mastery gradebook

fixes CNVS-13601

test plan
- create some outcome results with fractional scores (live
 assessments are great for this)
- view them in the student mastery gradebook
- ensure that the scores are rounded to two decimal places
- click to view the alignment details
- ensure that scores on the alignment details dialog are rounded

Change-Id: Ie46dd732597619c44479cb9c7000c0debe0aa2c0
Reviewed-on: https://gerrit.instructure.com/36380
Reviewed-by: Braden Anderson <braden@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Trevor deHaan <tdehaan@instructure.com>
Product-Review: Joel Hough <joel@instructure.com>