Edx-proctoring

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* Add a dropdown component.
* If the "data-enable-exam-resume-proctoring-improvements" data attribute on the element of the ProctoredExamAttemptView
Backbone is true,

* use the dropdown menu component on the Instructor Dashboard Proctored Exam Attempt panel for proctored exam attempts in the error state, providing the following options:

* Resume, which transitions the exam attempt into the ready_to_resume state.
* Reset, which behaves the same as the previous reset functionality, originally exposed via the [x] link.
* change the [x] link to Reset for exam attempts in other states.

* If the "data-enable-exam-resume-proctoring-improvements" data attribute on the element of the ProctoredExamAttemptView Backbone is
false there is no change.

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* Replace Travis CI with Github Actions.
* If a course has a proctoring escalation email set, emails that are sent when an
exam attempt is verified or rejected will contain that email address rather than a
link to support.

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* Allow staff users to modify another user's exam attempt status via the
the StudentProctoredExamAttempt view's PUT handler only when the action is
"mark_ready_to_resume" and the user ID is passed in via the request data.

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* Allow blank fields in Django admin for `external_id`, `due_date`, and `backend`
in proctored exams.

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* Added ProctoredExam to django admin

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* Added management command to update `is_attempt_active` field on review models