* simplifying edx.org breakpoints to use min-width
* creating -bp-* centric Sass variables
* converting all existing edx.org centric media queries to use new Sass variables

ECOM-1457

TNL-1660

TNL-1759

TNL-1502

TNL-1499

(SOL-531)(SOL-532)Course Cards update; A link to course discovery page has been added to the OpenEdX homepage

Update <nav> elements to correctly group links
for screen readers.

Fix RTL display issue with responsive header
on the login/registration page.

CSS background image was used for the home icon at upper right corner
so when user enter high contrast mode or disable bakground image it
disapear so moved it to DOM element

TNL-1382

TNL-1336

Fix link stylings in LMS and CMS footers

Allow configuration to override links to mobile app stores

Remove Jobs, News
Change "Vision" to "About"

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.

ECOM-406 removed commented out code, moved colours to variables and fixed hover state for mobile menu

 Made the header and footer responsive

Currently the .container and .wrapper-footer elements are set to 100%,
and also have horizontal padding added to them. This results in a total
width of greater than the full width of the viewport; This causing the
browser to scroll horizonally into empty space, regardless of how wide
the viewport is.

I had added the `box-sizing: border-box` to these elements in order to
resolve this.

Cheers,
Louis