improve performance of quiz index search box

we were previously re-rendering the list for every model changed. Now we only
render after the filtering is complete.

fixes CNVS-16247

test plan:
  - as a teacher
    - create a course with 30 or more quizzes
    - filter the quizzes using the search box at the top of the index page
    - It should filter the results much faster!!

Change-Id: Iafb0624a4974ff48223b87b2849c12476e098062
Reviewed-on: https://gerrit.instructure.com/43578
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Ryan Taylor <rtaylor@instructure.com>
QA-Review: Trevor deHaan <tdehaan@instructure.com>
Product-Review: Derek DeVries <ddevries@instructure.com>