add image accessibility best practice documentation URL and pass through to studio-frontend edit image modal

Also update studio-frontend to version 1.7.1

Open edit image modal via a custom signal

Send img tag attributes in open signal

Send natural image dimensions if no attr specified

Add new modal button in addition to old button

Also load built CSS when waffle switch on

Swap out TinyMCE toolbar button on waffle switch

Pass LANGUAGE_CODE from Django to template to studio-frontend

Define request.LANGUAGE_CODE in test_container_page.py

TNL-6060

TNL-4692

TNL-4160

TNL-4160

- Rename escape_json_dumps to dump_js_escaped_json
- Rename escape_js_string to js_escaped_string
- Update js_escaped_string to output empty string for None
- Introduce dump_html_escaped_json
- Move dump_js_escaped_json after the pipe as new best practice
- Introduce additional uses of helpers
- Introduce new djangolib directory and move js_utils

- 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

TNL-3822

Make escaping for json simpler and more consistent in Mako templates
- add escape_json_dumps to escape and json.dumps
- add escape_js_str to escape javascript string
- refactor Studio to use escape_json_dumps in Mako templates

TNL-2646: Escape json.dumps

TNL-2384

Refactored Studio's PagingView to use RequireJS Text and moved it
to common so that it can also be used by LMS.

TNL-1261

<nav> elements for the actions a user can perform on a perticular
page contain inaccessible label whic causes screen reader users
confusion regarding to their current navigation.

TNL-1531

TNL-652

It's a problem for accessibility

Admin ("Instructor") - Can edit and assign permissions to other users
Normal ("Staff") - Can edit
User - Can view the library and use content from it but cannot edit it or its blocks.

SOL-1, SOL-2, SOL-3

* updating vendor files
* updating class syntax (to new FA-based classes) for all UI elements
* correcting broken tests

TNL-997

[LMS-11372]
[LMS-11370]

STUD-2058

STUD-1856

Display "IS VISIBLE TO" when released and published

Reword staff lock prompt and notifications

Change "View Published Version" to "View Live Version"

Change "Unit Tree Location" to "Unit Location in Course"

Switch live content warning based on unpublished changes

Reword discard changes confirmation prompt

Reword unit location tip

Add "Edit the name" popup text for sections and subsections

Fix popup text for section and subsection titles

Add popup text for new section, subsection, and unit buttons

Reword popup for View Live button and add tests

Reword notification when removing staff lock

Update MessageView when has_changes changed

Change "Published" to "Published (not yet released)"

Change "Unpublished (Staff only)" to "Visible to Staff Only"