improve external tool return experience

test plan:
* create several types of external tool integrations
 (user navigation, account navigation, course navigation,
 external tool module items, external tool assignments, etc)
* when launching the tool in an iframe and finishing the tool use,
 instead of showing a generic "Tool Use Finished" page, it should
 break out of the iframe and redirect to another page

closes #CNVS-13800

Change-Id: I069e7052c819accc63f2bf546b46ff2db0c3afca
Reviewed-on: https://gerrit.instructure.com/39382
Reviewed-by: Brad Humphrey <brad@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>
Product-Review: Bracken Mosbacker <bracken@instructure.com>