move all DelayedJob Alert code into separate class

fixes CNVS-12411

test-plan:
regression test all alerts

Change-Id: Ie954c3c6c3f034fce130774c5c6e4e1515b02049
Reviewed-on: https://gerrit.instructure.com/33339
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Simon Williams <simon@instructure.com>
QA-Review: Jeremy Putnam <jeremyp@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>