In order to remove the deprecated flag_undefined_default=True
argument, this commit updates the following flags to always be
enabled using a new temporary class:

- course_experience.course_outline_page
- course_experience.unified_course_tab

Adds a temporary setting `USE_DEFAULT_TRUE_NAMESPACE`,
to enable a monitored rollout of this change.

TNL-7061 is the ticket where these flags will actually be
removed. This requires more careful work including removing
all dead code, and potentially refactoring tests that were
testing shared functionality, but only when the flag was
False.

ARCHBOM-1316

[BD-10] [DEPR-83]

Removed use of the 'shorten_welcome_message' waffle flag

AA-108

If a course welcome message is very long, cut it off with an
ellipsis and show a Show More button to reveal the full thing.

AA-46

Switch from a separate waffle flag for the dates widget v2 work
and just use the relative dates experiment flag instead.

This is a helpful class when running an experiment, to help
bucket users and keep track of which enrollments to consider
as part of the experiment.

AA-53

Specifically, course_experience.relative_dates. This will be used
by future PRs to control our rollout of this new feature.

AA-27

This will remove imports from __future__ that are no longer needed.

https://docs.python.org/3.5/library/2to3.html#2to3fixer-future

The course_visiblity field can have one of three values:
1. private (default): This keeps the standard access rules.
2. public_outline: Allows unenrolled and anonymous users access to the outline.
3. public: Allows unenrolled and anonymous users access to both outline and
   course content.

When an unenrolled user accesses course content, instead of student_view(),
public_view() is used. A default implementation is provided for XBlocks
which do not implement this view. The public_view() must not have any
functionality which assumes the presence of a valid User and should show
a readonly only interface for the XBlock content.

This reverts commit f9ae594d, reversing
changes made to 7c08e50f.

The course_visiblity field can have one of three values:
1. private (default): This keeps the standard access rules.
2. public_outline: Allows unenrolled and anonymous users access to the outline.
3. public: Allows unenrolled and anonymous users access to both outline and
   course content.

When an unenrolled user accesses course content, instead of student_view(),
public_view() is used. A default implementation is provided for XBlocks
which do not implement this view. The public_view() must not have any
functionality which assumes the presence of a valid User and should show
a readonly only interface for the XBlock content.

This patch would remove CourseListView slow transaction by changing
CourseWaffleFlag to WaffleFlag. This removes extra hit on
WaffleUtil's model (WaffleFlagCourseOverrideModel).

LEARNER-5566

LEARNER-1694

Fix a11y failure

Fix header styling

Fix layout issues

Further layout fixes

LEARNER-2073

LEARNER-2307

Audit learners are now shown a prompt to upgrade to the verified track
of the course run. This message goes away after the learner upgrades.

LEARNER-1894

This commit adds in course messaging for three use cases. First,
when the user is not signed in, the user is shown a message that
provides a link to sign in or register. If the user is signed in
but not enrolled, they are given a link to do so. If the user is
enrolled but the course has not yet started, they are shown a
message explaining when the course starts and shown a link (not
yet enabled) to add a reminder to their calendar.

The implementation defines a base message class and extends it
for the course home messages as well as the previously implemented
page level messages.

LEARNER-1854

This includes several general enhancement in addition
to the fixes for unified_course_view:
1. Add support for default when no waffle flag defined.
2. Add support for table_blacklist to assertNumQueries.
3. Rename flag to 'course_experience.course_outline_page'.
4. Change flag default to True when it is not defined.

Adding a reviews page to the course and updating the reviews module on the course about page. Removed the existing coursetalk implementation and put it in a fragment, removed the tests as well. Added configuration settings to specify the reviews template as well as the reviews provider. This is all protected by a waffle flag.

This sock sits at the bottom of both the home and the course content pages. It allows the user to click a 'Learn More' button to open a panel that allows the user to navigate to the upgrade checkout page. The sock is only shown for users that have not yet upgraded in a course that has a verification upgrade date that has not yet passed. Python tests cover the various course mode and upgrade dates.

LEARNER-877

LEARNER-879

LEARNER-609

LEARNER-607

LEARNER-606