Revert "Basic architecture of Maintenance App - SUST-19, SUST-42. Implement Force Publish Course view. SUST-46"

This reverts commit 27646b7e.

Removed the Darklang preview-lang and clear-lang parameters and added the new DarkLang settings form at /update_lang

Remove the DarkLang middleware from the LMS

Created and basic routing to the update_lang page for the GET Request
TNL-4742

Basic form functionality

Working example in LMS of the form to set the language

Login now required to change the preview language, and corrected some minor bugs

Updates to move the template code to lms and to correct minor defects
TNL-4742

Added template for preview_lang.html to cms
TNL-4742

Changed filename of darklang.py to api.py to match convention
TNL-4742

Updated and refactored the Darklang tests
TNL-4742

Updated comments in tests
TNL-4742

Formating updates
TNL-4742

Updated comments and formatting
TNL-4742

Corrected i18n tests and corrected PEP8 format issues
TNL-4742

Code Lint/PEP-8 corrections and upates
TNL-4742

Removed constant that was not needed (to be squashed)
TNL-4742

Added init method to clear up PEP8 Warnings (will squash)
TNL-4742

PEP-8/Lint issue resolved (squash)

Updated for i18n
TNL-4742

Refactored the preview_lang.html page to use a common included template

Refactoring and changes from PR comments
TNL-4742

Correction for safecommit violation (Squash)
TNL-4742

PR changes and refactoring (Squash)

Updates to reduce changes made in the urls used
TNL-4742

Removed unneeded aria-described by and bug in MAKO Template (squash)
TNK-4742

Updated docstring comments

Clarified form response text

Minor PR request (Squash)

Refactoring of how the responses are generated within the DarkLang views file

A series of refactors in response to PR comments

Method name change for clarity in reponse to PR comments (Squash)

Updates to tests per PR requests (Squash)

Minor comment updates for clarity and PR requests (Squash)

Updated per PR comments and added a test for empty preview_language

Layout and code style updates (Squash)

Updated test to contain method in the request.

Removed the Darklang preview-lang and clear-lang parameters and added the new DarkLang settings form at /update_lang

Refactored tests and added some tests for coverage, corrected defect with empty input codes

Removed unused and obsolete code

Corrected test errors, resolved PR comments, and updated comments to clarify testing
TNL-4742

Updated tests to deal with Pylint quality issue (Squash)

Updated tests to better reflect test case and PR updates (Squash)

The LMS continues to expect lowercased category slugs, while the Studio program creator now uses correctly cased slugs. Programs should be updated before this is released. Part of ECOM-5018.

Basic architecture of Maintenance App - SUST-19, SUST-42. Implement Force Publish Course view. SUST-46

TNL-4670

TNL-4906 Subsections now use radio buttons, to allow for "hide after due" as a
visibility option. Also, all tabs have been consolidated to "Basic" and
"Advanced", and visibility options have moved there.

Documentation links are updated to assist course authors with the new
visibility options. Tests have also been updated, and the changes suggested
in TNL-4951 are included.

Remove edx-icons from edx-platform - TNL-4813
Remove edx-icons from LMS - TNL-4952
comment out baseline screenshot Bokchoy assertion tests
SOL-1937 Temporarily comment out baseline screenshot Bokchoy assertion tests

TNL-4805

TNL-4799

TNL-4692

show Save and Cancel button when admin change Instructor image asset path from Studio schedule and details page

show_children_previews was not being evaluated before

TNL-4366
Changes in studio to allow the hide_after_due setting to be utilized.

Includes:
    -python changes to contentstore, where the data is stored.
    -refactoring of timed-examination-preference-editor.underscore, to add this
        setting and make the editor more accessible.
    -javascript changes to link the new setting to the correct data model.
    -sass updates to fix a11y issues on the editor modal.
    -addition of post-due visibility information to course outline in studio.
    -new tests: python, js, acceptance, and a11y

TNL-4366
Changes in studio to allow the hide_after_due setting to be utilized.

Includes:
    -python changes to contentstore, where the data is stored.
    -refactoring of timed-examination-preference-editor.underscore, to add this
        setting and make the editor more accessible.
    -javascript changes to link the new setting to the correct data model.
    -sass updates to fix a11y issues on the editor modal.
    -addition of post-due visibility information to course outline in studio.
    -new tests: python, js, acceptance, and a11y