Course Blocks App MA-1556

Fixes for chrome automation:

Add response times to get_many/set_many/delete_many.

Update translations (autogenerated message)

Clytwynec/add paver test a11y

adds an accessible label to the search input and the search button

Updated Zendesk error handling

Fix date summary blocks for courses without an end date.

MA-1044 DiscussionTopic - Added bulk operations

Remove legacy MITX_FEATURES reference

Properly logging exceptions so we have the complete stacktrace.

ECOM-2792

SOL-1377: allow certifcate exception to be added for multiple courses

Added checkout error page.

Upgrade draggabilly.js to fix Firefox iframe bug

added unit test to test certs exception same user different courses scenario

Allow bok-choy default_store to be controlled by env vars.

TNL-3627

Refactor for multiprocessing.

I also took this opportunity to do some small cleanups of the date
summary code, specifically converting some attributes to properties in
order to remove a Pylint directive disabling warnings about missing
docstrings.

* We do not need to click the upload button twice (typo?)
* Using a non-unique name for the upload image is causing GridFS indexing errors when
run too closely together (which happens with Chrome's speed)

(WIP) Proctoring: fix sass and use updated edx-proctoring version

ECOM-2516

SOL-1346:convert string to bytestring before passing it to urllib.quote_plus