Replace `check_for_get_code` with `assert_request_status_code`

More flexible, uses the word "assert", method instead of function
Refactor LMS Video Tests
Decrease Video Player Init Wait Timeout
make expanding explanation accessible

LMS-11161
Toggle aria-expanded attribute
Merge pull request #4715 from edx/ammar/decrease-video-player-init-timeout

Decrease Video Player Init Wait Timeout
Merge pull request #4261 from edx/ammar/video-tests-refactoring

Refactor Bok-Choy LMS Video Tests
Fix property call issue
Merge pull request #4731 from edx/ammar/fix-property-call

Fix property call issue
Catch InvalidKeyError in UserTagsEventContextMiddleware.

LMS-11189
Catch InvalidKeyError in static_tab view.

LMS-11189
Merge pull request #4678 from edx/usman/lms11189-user-api-middleware-exception-2

Catch InvalidKeyError in UserTagsEventContextMiddleware and static_tab view.
Merge pull request #4654 from edx/db/kill-check-for-code

Replace `check_for_get_code` with `assert_request_status_code`
Merge pull request #4602 from edx/db/expand-on-click-or-enter

make expanding explanation accessible
show upload progress on import course view
STUD-2017

update import upload gui
Do not show timeout message during import and continue pinging for status.

STUD-2017
make import ui more robust + save import status in session for each state
add log and comments
Not to be merged into master! Updated gunicorn and added timeout.