Putting the new edx header behind a feature flag.

Reuse the style from login and register views.
Remove all the specific style.

- 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

With tests, some settings changes
(all should default to not breaking anything for edx)

Added styling for shopping cart User Experience
- Styled shoppingcart list page
- Styled navigation shopping cart button
- Styled receipt page
- Styled course about page for shopping cart courses

Addressed HTML/SCSS issues

Remove offending body class and unnecessary sass changes

Addresses many review comments on stanford shopping cart

* framework for generating order instructions on receipt page
  in shoppingcart.models
* move user_cart_has_item into shoppingcart.models
* move min_course_price_for_currency into course_modes.models
* remove auto activation on purchase
* 2-space indents in templates
* etc

revert indentation on navigation.html for ease of review

pep8 pylint

move logging/error handling from shoppingcart view to model

Addressing @dave changes

LMS/Accounts: Converts many class-based Sass archetype-focused @extends to use Sass placeholder syntax

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

theming - revised variables and link/button styling to account for edX's registration and login constrast/styling changes

edx.org redesign - revised temporary login/register views to fit with design requirements/fixes from marketing team's overall design changes to site's visual theme

Firefox doesn't draw the buttons right with -90deg, but will draw it right if no direction is specified.

drupal integration - revised/proofed header and footer styles to match spacing of marketing site and renamed social icons

drupal integration - revised general header HTML and Sass to coincide with marketing site nav and theme

Rearranged more images, made some smaller, made some slight changes to the design on the homepage and made all edX proper case

renames some scss files for better orginization, sets fixed widths on main containers to avoid akward scaling issues untill media queries can be added for more responsive scaling

adds pressrelease page, breaks about content into seperate pages, imporvoves some visual elements of about and jobs pages