fix lock/unlock date ranges for assignment overrides

after a discussion with product/design we decided to get rid of the fancy date
range since it is likely that they have 'only' a lock or unlock date. Instead
we're going to put these in a table like it does in the non-fabulous version

fixes CNVS-12872

test plan
- as a teacher
  - create a quiz with multiple dates for various sections
  - add a date for a section with only a lock date
  - add a date for a section with only an unlock date
  - add a date for a section with both a lock and unlock date
  - make sure they all continue to look nice and display similar to they do now
    in the non-fabulous version

Change-Id: I6d76848fa20955757b018ed853a373e18608acc3
Reviewed-on: https://gerrit.instructure.com/34746
Reviewed-by: Jason Madsen <jmadsen@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Product-Review: Derek DeVries <ddevries@instructure.com>