link subject to submission in submission comment inbox

fixes CNVS-16948

test plan
- view a submission comment in the submission comment inbox
- ensure that the subject in the message detail view (right side
 display) links to the submission comment

Change-Id: I2ea4bd8c44a52ff6a250b83638b4d9a2556617d0
Reviewed-on: https://gerrit.instructure.com/44541
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Janelle Seegmiller <jseegmiller@instructure.com>
Reviewed-by: Brad Horrocks <bhorrocks@instructure.com>
QA-Review: Steven Shepherd <sshepherd@instructure.com>