add lti2 models and registration endpoints

fixes PLAT-522 PLAT-429 PLAT-545 PLAT-540 PLAT-498

test-plan
you can register an lti2 tool

Change-Id: If045b694213e1019f8a595b63a7e33ea4ac28e64
Reviewed-on: https://gerrit.instructure.com/37095
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>
Reviewed-by: Brad Humphrey <brad@instructure.com>