move lti registration endpoint to new message controller

fixes PLAT-567

test-plan:
specs should pass

Change-Id: I1a38910ddb3cf52319f4d38a71c3d075da79693d
Reviewed-on: https://gerrit.instructure.com/38612
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Brad Humphrey <brad@instructure.com>
Product-Review: Nathan Mills <nathanm@instructure.com>
QA-Review: Nathan Mills <nathanm@instructure.com>