parse cc assignment extension data

test plan:
* importing the example package with cc assignment data
 should bring in canvas specific assignment data (like grading type)

* cc and canvas package import regressions

closes #CNVS-13270

Change-Id: Ic053837aa7642212bc0360f5e5ecf2cd27a88d9b
Reviewed-on: https://gerrit.instructure.com/35747
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Bracken Mosbacker <bracken@instructure.com>
Product-Review: Bracken Mosbacker <bracken@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>