ECOM-7099

There are a number of Django Signals that are on the modulestore's
SignalHandler class, such as SignalHandler.course_published. These
signals can trigger very expensive processes to occur, such as course
overview or block structures generation. Most of the time, the test
author doesn't care about these side-effects.

This commit does a few things:

* Converts the signals on SignalHandler to be instances of a new
  SwitchedSignal class, that allows signal sending to be disabled.

* Creates a SignalIsolationMixin helper similar in spirit to the
  CacheIsolationMixin, and adds it to the ModuleStoreIsolationMixin
  (and thus to ModuleStoreTestCase and SharedModuleStoreTestCase).

* Converts our various tests to use this new mechanism. In some cases,
  this means adjusting query counts downwards because they no longer
  have to account for publishing listener actions.

Modulestore generated signals are now muted by default during test runs.
Calls to send() them will result in no-ops. You can choose to enable
specific signals for a given subclass of ModuleStoreTestCase or
SharedModuleStoreTestCase by specifying an ENABLED_SIGNALS class
attribute, like the following example:

    from xmodule.modulestore.tests.django_utils import ModuleStoreTestCase

    class MyPublishTestCase(ModuleStoreTestCase):
        ENABLED_SIGNALS = ['course_published', 'pre_publish']

You should take great care when disabling signals outside of a
ModuleStoreTestCase or SharedModuleStoreTestCase, since they can leak
out into other tests. Be sure to always clean up, and never disable
signals outside of testing. Because signals are essentially process
globals, it can have a lot of unpleasant side-effects if we start
mucking around with them during live requests.

Overall, this change has cut the total test execution time for
edx-platform by a bit over a third, though we still spend a lot in
pre-test setup during our test builds.

[PERF-413]

Hackathon XV project

ECOM-5936

ECOM-4763

This reverts commit 21746f1e.

ECOM-4763

ECOM-4214

* mattdrayer: Add bulk checkout link to course views
* asadiqbal08: MAYN-225 replace the "Verify Now" button by the "Go to Dashboard" button in case of themed sites.
* mattdrayer: Add bulk_sku check in courseware.views

* mattdrayer: Add bulk checkout link to course views
* asadiqbal08: MAYN-225 replace the "Verify Now" button by the "Go to Dashboard" button in case of themed sites.
* mattdrayer: Add bulk_sku check in courseware.views

By default, disable all caching in tests, to preserve test independence.
In order to enable caching, inherit from CacheSetupMixin, and specify
which cache configuration is needed.

[EV-32]

The TestCase API doesn't accept arguments, so passing arguments for some
TestCase subclasses makes adding new inheritance/mixins tricky. Instead,
prefer configuration via class attributes for TestCases.

More accurately, this creates a 4th shard because the
last shard is always the default.

More accurately, this creates a 4th shard because the
last shard is always the default.

Our current sandbox provisioning uses a create_user management command,
which creates and enrolls a user into a course. However, for TE-1128, we
will need a way to enroll the same user to multiple courses (which are
dynamic at time of provisioning). Using the existing management
command is no longer feasible for that, so we are using one that accesses
the enrollment API, which is the new standard for new enrollment capabilities.

This reverts commit 3149aaa3.

This allows the edX REST API Client to perform a sucessful GET against
this API, since Slumber (which our client is based off of) appends the
trailing slash by default.

TNL-2180

ECOM-2972

Please note that this is a squshed commit and the work of:
Symbolist, macdiesel, nedbat, doctoryes, muzaffaryousaf and muhammad-ammar

Also remove useless docstrings where they were added to keep pylint
quiet.

https://github.com/edx/edx-platform/pull/9345

* Upgrade edx-submissions
* Upgrade edx-ora2
* Upgrade edx-val
* Upgrade edx-proctoring
* Update all edx-platform code that depends on DRF, including:
  - auth_exchange
  - cors_csrf
  - embargo
  - enrollment
  - util
  - commerce
  - course_structure
  - discussion_api
  - mobile_api
  - notifier_api
  - teams
  - credit
  - profile_images
  - user_api
  - lib/api (OAuth2 and pagination)

* Upgrade edx-submissions
* Upgrade edx-ora2
* Upgrade edx-val
* Upgrade edx-proctoring
* Update all edx-platform code that depends on DRF, including:
  - auth_exchange
  - cors_csrf
  - embargo
  - enrollment
  - util
  - commerce
  - course_structure
  - discussion_api
  - mobile_api
  - notifier_api
  - teams
  - credit
  - profile_images
  - user_api
  - lib/api (OAuth2 and pagination)