Converts the dates on the dashboard, sidebar navigation, and important course dates to user specified time zone.

TNL-4622

Following have been done
1- Change the structure of the course navigation Menu HTML
2- Add some basic styling
3- Add basic JS for html rendering
4- Update tests according to new structure

AC-76

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.

TNL-892

Removed inappropriate section tags. Because screen readers announce each section, they should not be used unless they are actually defining meaningful sections.

- 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