export media comments from copied courses

test plan:
 - attach media comments to a course
 - copy the course
 - export the copy
 - import the package
 - the media comments should be preserved

fixes CNVS-12228

Change-Id: Ie200d65c77856ac0cd8a694c8cb4fb56558cf260
Reviewed-on: https://gerrit.instructure.com/32975
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Bracken Mosbacker <bracken@instructure.com>
Product-Review: Bracken Mosbacker <bracken@instructure.com>
QA-Review: Matt Fairbourn <mfairbourn@instructure.com>