TNL-4622

ECOM-3799

ECOM-2810

This is a squash of 38 commits ending with
5b080f979d692804452400ac5bed9b17c50b001e

Iniital refactor of capa styling for basic checkbox and multiple choice problem types, including additional comments to sass styles

Use native checkboxes for courseware license options
In Studio settings editor for video module, don't show license if feature-flagged off
Don't let Scope.contents fields leak to Studio editor
JS gettext() must all be on the same line for i18n
Add docstrings for bok-choy tests
Remove LicenseMixin from HTMLDescriptor
Responding to UX review feedback
Add aria-pressed attribute
Use https links instead of protocol-relative links for links to creativecommons.org
Remove license from course outline page in Studio

SASS compilation variable conventions update, focusing on basic colors, baseline variable usage for padding and margins, ui-depth extends, along with other small fixes. The intent with this is to not have any user-facing impact, and instead move us closer toward having files that use our newer sass conventions.

- Doubled up :hover and :focus styling to improve a11y
- Increase contrast of certain UI elements for improved a11y
- Added some image alt text for a11y
- Changed video caption styling to blue and made them underline on hover and added a skip link before video for screenreaders.

Fixes Bugs:
- LMS-1336

Bourbon's box-shadow mixin has been deprecated, and they recommend to use the
official spec.

The official border-radius mixins were deprecated and removed in Bourbon 3.0.
https://github.com/thoughtbot/bourbon/pull/95

- removed ::selection css from reset.scss
- removed variables from variables.scss
- removed variable calls from course/base/base.scss and base/base.scss

Stanford got some feedback from our students/faculty that students
were making accidental clicks on radio-button capa questions.
They would click way to the right of the label text, but it would
still select the corresponding input, which caused some students
to make unintentional changes to their answers.  This was because
labels for these inputs were display:block and width:100%

Changing these labels to float:left clear:both should fix it.

revised no certificate state for dashboard messages and removed course message UI for future work on separate branch

This reverts commit 2b5e8a49, reversing
changes made to db0549be.