adds graph cluster detection

Change-Id: I83ec95a69a8f01f682ddc8f75fc0e8f0e66ee5ab
Reviewed-on: https://gerrit.instructure.com/45455
Reviewed-by: Coraline Ehmke <coraline@instructure.com>
Product-Review: Michael Ziwisky <mziwisky@instructure.com>
QA-Review: Michael Ziwisky <mziwisky@instructure.com>
Tested-by: Michael Ziwisky <mziwisky@instructure.com>