This commit "undoes"a previous hotfix, and allows a cms course_publish
signal to trigger a block_structure update_course_in_cache task, which
is run on an lms worker queue.

Changes:
    -exposes ALTERNATE_QUEUE_ENVS
    -adds routing layer in celery.py
    -moves prior dev_with_worker settings file to devstack_with_worker
    -moves course_block api functionality into openedx/core/djangoapps/content/block_structure

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]

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.

ECOM-3994

We don't want to blindly assemble the base CDN URL with whatever an
image URL happens to be, since it might be an absolute URL and now the
result is a broken URL.  We take a more selective approach now.

This will leverage the nose attrib plugin to allow us
to break tests apart on our build system to run
in parallel on separate nodes.

Unfortunately, instrospection.get_table_description runs
select * from course_overview_courseoverview, which of course
does not exist while django is calculating initial migrations, causing
this to fail.  Additionally, sqlite does not support information_schema,
but does not do a select * from the table.

Lift the main part of mysql's get_table_description up to the migration itself
and just inspect it directly.  Continue to call the API for sqlite.

We removed a column in the same release that we removed it
from the model.  This creates a gap where the code still looks for
a column which has been dropped until the new code has been deployed.

The initial fix was to put the column back, but that creates a window
during the alterations where views will error.

This noops the 0008 migration and effectively noops 0009 unless you've
run the old migration.

Previously, course images on the student dashboard were always
served from the localhost, even if the CDN was enabled.

Cached values were leaking across tests, causing difficult to debug errors,
particularly when using Config Models. As part of this work, certain tests
that had query counts that relied on those values being cached needed to
be adjusted up.

MA-1368

It somehow ended up in CourseOverviewImageSetTestCase (merge artifact?).

Without this change, we'd throw a TransactionManagementError in the case
where we have a race condition and generate multiple CourseOverviewImageSets
for the same CourseOverview concurrently.

- Remove escaping in display_name_with_default
- Move escaped version to deprecated display_name_with_default_escaped
- Does not include any other changes to remove double-escaping

Thanks to agaylard who initiated this work:
https://github.com/edx/edx-platform/pull/10756

TNL-3425

Course teams occasionally upload very large files as their course
image. Before this commit, those images would be used directly in
the student's dashboard, sometimes leading to MBs worth of image
data on that page. With this commit, we now auto-generate small
and large thumbnails of configurable size. The Student Dashboard
and Course About pages will make use of this new functionality
(CourseOverview.image_urls), but the behavior of
CourseOverview.course_image_url will not change.

Note that the thumbnails are still created in the contentstore,
and sit alongside their originals.

What's included:

1. Multiple sizes, currently starting with "raw", "small", and
   "large". This falls back to the current behavior automatically in
   the case where thumbnails don't exist or this feature has been
   disabled in configuration.

2. Django admin based configuration for image sizes and whether
   to enable the functionality at all. Note that to regenerate
   images, you'd need to wipe the CourseOverviewImageSet model
   rows -- it doesn't do that automatically. This is partly because
   it's a very rare operation, and partly because I'm not entirely
   sure what the longer term invalidation strategy should be in a
   world where we might potentially have multiple themes. The
   flexible configuration was intended to allow better customization
   and theming.

3. The Course About pages also use the new thumbnail functionality,
   as an example of "large". This is in addition to the "small"
   used on the student dashboard.

Things I'm punting on for now (followup PRs welcome!):

1. Bringing the thumbnails to course discovery. A quick attempt
   to do so showed that it wasn't getting properly invalidated
   and updated when publishes happen (so the old image still showed
   up). It probably has something to do with when we do the
   re-indexing because it stores this data in elasticsearch, but
   I'm not going to chase it down right now.

2. Center-cropping. While this is a nice-to-have feature, the
   behavior in this PR is no worse than what already exists in
   master in terms of image distortion (letting the browser handle
   it).

3. Automated invalidation of the images when a new config is
   created.

Org to filter by is provided to the Course API list view using a querystring argument. Filtering ultimately occurs at the database layer. ECOM-2761.

Added the following fields to CourseOverview:
    announcement
    catalog_visibility
    course_video_url
    effort
    short_description

Now requires CourseOverview models for each course in the system:
    Introduced a CourseOverviewGeneratedHistory model to keep track of
    when the CourseOverview table was seeded. The seeding can be
    done preemptively by calling the generate_course_overview management
    command. Otherwise, it is lazily computed, when needed.

CCX overrides course max_student_enrollments_allowed
and set it to 200 during CCX creation

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

This will allow v1 code of CourseOverview to delete entries. While
this is not a good thing in general (and future versions will ignore
entries with higher versions than they support), this is necessary
to prevent errors with the existing code in a rollback situation.
Otherwise, old code trying to delete CourseOverview entries will
fail with a foreign key constraint violation.

Previously, CourseOverview would delete data for any version
that didn't match the current one. That could cause problems
during deploys, when multiple versions of CourseOverview
were active. They would overwrite each other, and that could
cause problems if the old one overwrote the new one -- in
our case, the new one created a new table with foreign key
links that the old one was unaware of, and trying to delete
it would have caused an error.

* Fix paver violations to stablize edx-lint update
* Parens, Line2Long
* Fix missing docstrings
* Fix PEP8 issues
* Address PR feedback (thanks @nedbat!)

Preserve DRF v2 behavior of defaulting to None
for missing keys in the grading policy dictionary.