* added generate certificates task and bok choy tests
* added unit tests
* changes based feedback and improved acceptance test
* Change header text
* changes based on feedback on 24/6
* added task_id to api output
* fixed broken test
* Remove "Instructor" from strings, per Docs team
* Fixed flaky entrance exam test

Allow global staff to generate example certificates
on the instructor dashboard.

Allow global staff to enable/disable self-generated
certificates for a course.