This PR solves the DeprecationWarning mentioned in:
https://build.testeng.edx.org/job/edx-platform-python-pipeline-master/warning_5freport_5fall_2ehtml/

HTMLParser was renamed in html.parser in Python3:
https://docs.python.org/2/library/htmlparser.html#module-HTMLParser

* html_parser.HTMLParser().unescape from six.moves has been deprecated

* instead use html.unescape from Python3

Documentation for unescape in Python3:
https://docs.python.org/3/library/html.html#html.unescape

- html_parser from six.moves has been deprecated

- instead use html.parser from Python3

- Order imports using isort

- Delete unused import crum

[BD-6] Use Pypi release of social-app-django

Move social-app-django from github to base requirement, since PyPi version is now compatible with the platform.

* Commits:
  Update masquerade API to show only active partitions
  Add explicit masquerade support to courseware API

* Commits:
  Replace references to 'log.warn' with 'log.warning'

all versions updates were minor and no visible downgrades

Fixing 56 GuessedAtParserWarnings, in commit edx#24098

Background: BeautifulSoup automatically picks the fastest parser available. By default, it picks the "lxml" parser.

Per the [BeautifulSoup](https://www.crummy.com/software/BeautifulSoup/bs4/doc/#installing-a-parser) documentation:

> Beautiful Soup supports the HTML parser included in Python’s standard library, but it also supports a number of third-party Python parsers. One is the lxml parser. Depending on your setup, you might install lxml with one of these commands.
> Another alternative is the pure-Python html5lib parser, which parses HTML the way a web browser does. 

Context: We changed two statements, one in lms and another in openedx. Both statements fire up BeautifulSoup. Now we explicitly ask for "lxml," following the recommendation on BeautifulSoup's documentation:

> If you can, I recommend you install and use lxml for speed. If you’re using a very old version of Python – earlier than 2.7.3 or 3.2.2 – it’s essential that you install lxml or html5lib. Python’s built-in HTML parser is just not very good in those old versions.

Before:
`soup = BeautifulSoup(content)`

After:
`soup = BeautifulSoup(markup=content, features="lxml")`

The warnings are gone, tests are passing in local.

* Hide private team-sets from users not on a team

* Modify add team count to factor in team visibility

* Fix bug that broke search w/in private team-sets

to remove some `DeprecationWarning`s from the logs
as the former method as been deprecated since Python 3.3 [1][2].

- [1] https://github.com/python/cpython/blob/3.3/Lib/logging/__init__.py#L1252-L1253
- [2] https://stackoverflow.com/a/15655674

update version of edx-proctoring library

Fix Dates Banner Translations

If setting ENABLE_WAFFLE_FLAG_METRIC is True, a custom
metric will be added with the values of all WaffleFlag
and CourseWaffleFlags seen during the transaction.

Metric flag values could be False, True, or Both.
The value Both would mean that the flag had both
a True and False value at different times through
the transaction. This is most likely due to having a
check_before_waffle_callback, as is the case with
CourseWaffleFlag.

Example metric value:

    "{'another.course.flag': 'False', 'some.flag': 'False', 'some.course.flag': 'Both'}"

Warning: NewRelic does not recommend large custom
metric values due to the potential performance
impact on the agent, so you may just want to
enable when researching usage of a particular flag.
Metric values longer than 255 are truncated.

TODO: A how_to can be added later if we find this
useful, including helpful querying tips.

ARCHBOM-132

- replace unicode apostrophes with single quotes in dates banner.
- change language in button from 'Reset my deadlines' to 'Shift
  due dates'

* use external_user_key in teams csv download

AA-137: Support courseware celebrations

[BD-10] Remove unused course sock URL.

[BD-10] [DEPR-68][DEPR-84] Remove pattern library of learner_dashboard/programs.py

[BD-10] [DEPR-79] Remove pattern library of mobile/course-dates-fragment.html

[BD-10] [DEPR-70] Remove waffle flag edx_discussions.use_bootstrap. 

[BD-10] [DEPR-78][DEPR-82] Remove pattern library of latest-update-fragment.html and welcome-message-fragment.html

[BD-6] Fix python 3.8 compatibility

Mergeback PR from private to public.

Sustaining xsslint security fixes

[BD-10] [DEPR-83]

Removed confirm email after SSO

- Add a new CourseEnrollmentCelebration model, which ties a
  course enrollment to some booleans about progress celebrations
- Add serialization of the new model to the existing courseware_api
  app's existing course info view
- Add new API in courseware_api to update a celebration model