Change the automatic username

[stemar]

Lti13::getUsername() Line 500

I don't think this is a good username

In other projects, he have a setting variable that allows you to select which LTI launch parameter is used for setting certain fields. I think the username is supported to be the CWL in iPeer but it would still need to be configurable for other institutions.

Originally posted by @andrew-gardener in https://github.com/_render_node/MDE3OlB1bGxSZXF1ZXN0UmV2aWV3NDExMTM4MDY5/pull_request_reviews/more_threads