* fix: pin python-slugify<5.0.0
transifex-client requires python-slugify<5.0.0 for Python 2.0 support which conflicts with the latest python-slugify version.
This was to support an experiment in using coverage test contexts to
record what tests ran each line of code (informally known as
who-tests-what, or wtw). It never became operational.
* Deletes custom get_search_results() method, since `enterprise_customer__name` is now a viable search field
* Improves pagination by asking for an estimated row count from Mysql INFORMATION_SCHEMA.TABLES
* Turns 1 + N query into 1 query via proper use of list_select_related
ENT-4384
JIRA: MST-736
Due to inconsistencies in the way we handle attempts in past due practice proctored/onboarding exams, learners can end up in an unintended liminal state after attempting to reset their onboarding attempt. If a learner attempts to reset their rejected onboarding attempt after the exam's due date, we process the reset request and move their attempt into the "onboarding_reset" state. Theoretically, a new exam attempt should be created immediately thereafter. However, we have code that prevents the creation of an exam attempt after the exam's due date, so the call to create a subsequent exam attempt fails, leaving the learner with an exam attempt with the "onboarding_reset" status. Theoretically, this situation should never occur, and the fact that it does is a bug. Because of this, we did not handle the "onboarding_reset" status in the StudentOnboardingStatus panel, and this status appears as "null". As an intermediate step, while we think about our due date logic, this pull request bumps the edx-proctoring library to version 3.8.5, which adds a new onboarding status "onboarding_status_past_due". This status is displayed as "Onboarding Reset Failed Due to Past Due Exam" in the StudentOnboardingPanel in the InstructorDashboard, which should provide course staff with a clearer explanation.
JIRA: MST-745 tracks the removal of this intermediate code from the code base once we fix the underlying cause of this bug.
JIRA: MST-749 tracks the fix for the behavior that allowed for this state to occur.
This:
1. Introduces a new override using the `pluggable_override` decorator.
It is now possible to specify a custom way of getting XBlock's icon
by defining `GET_UNIT_ICON_IMPL` in settings.
2. Introduces a way to add custom `XBLOCK_MIXINS` by defining
`XBLOCK_EXTRA_MIXINS` in settings. This allows, e.g. to add
new fields to XBlocks.
* MST-734 Fix production issue on Learner Onboarding Status Panel
Fix the prod issue where learning sequence service object missing the needed get_user_course_outline service API
The user web API call currently returns 500
