pretty assignment edit page

fixes CNVS-10347

test plan:
general regression test of assignment edit page with draft state on and
off.

general regression test of discussion edit page.

Change-Id: I54e75f55f8acc604998e36c879d98b8a1176c817
Reviewed-on: https://gerrit.instructure.com/28714
Reviewed-by: Mike Nomitch <mnomitch@instructure.com>
Product-Review: Mike Nomitch <mnomitch@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Amber Taniuchi <amber@instructure.com>