Serve branded footer JSON/HTML/CSS/JS from an API endpoint
in the branding app.  Refactor OpenEdX and EdX.org footer templates
to use the Python version of the API, ensuring that the API
values are consistent with the footer included in main.html.

Detailed changes:

* Added footer API end-point to the branding app.
* Footer API allows the language to be set with querystring parameters.
* Footer API allows showing/hiding of the OpenEdX logo using querystring parameters.
* Deprecate ENABLE_FOOTER_V3 in favor of the branding API configuration flag.
* Move no referrer script into main.html from the edx footer template.
* Rename rwd_header_footer.js to rwd_header.js
* Cache API responses.

Authors:
Awais Qureshi, Aamir Khan, Will Daly

ECOM-1547 created new template and Sass file for new footer. Wrapped it in a feature flag and updated previously named footer-edx-new.html to footer-edx-v2.html to better track/name updates to the footer going forward.
ECOM-1547 removed data-updated attributes from body
ECOM-1548 added JS file that inits analytics event listener and makes ajax call to API to get footer and HTML and add it to the DOM
ECOM-1547 code review cleanup
ECOM-1547 rebase and Sass appraoch update after @talbs the IE9 killer slayed the mighty beast.
ECOM-1547 updated file names and added comments in light of @talbs review of PR
ECOM-1547 update to social media link styles and nav link order
ECOM-1547 updated SOCIAL_MEDIA_FOOTER_NAMES if ENABLE_FOOTER_V3 is true
ECOM-1547 added translations to screenreader text
ECOM-1547 fixed test and renamed files in line with @talbs's pending PR
ECOM-1547 cleaned up file naming

Replaces some PLATFORM_* settings with a more
general setting for specifying social media
URLs in the footer.

Adds icons and titles for new social media
sites (Tumblr, Reddit, Youtube) to match
EdX.org.

Fix link stylings in LMS and CMS footers

[OPEN-444]

Allow configuration to override links to mobile app stores

OPEN-307

OPEN-307

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

LMS-6617

Fixed wiki merge url regex.
TNL-413

ECOM-345 changed any lists that could display with only 1 item to divs

ECOM-345 Added aria tags for header

ECOM-364 Accessibility update for footer

added my name to the authors file

Addressing feedback from code review - removing unnecessary element references in selectors

Updated header aria-label to be main

Move the open edx logo inside the div

Adding a bunch of placeholder views.

indenting.

Making some styles work against LMS sass.

Adding back the old edx footer and associated icons, with a feature flag.

We need to use an Open edX footer by default (and that's what all non-edx.org
instances should base their footer off) and only use the edX footer on
edx.org.

This commit uses `SITE_NAME` to determine which footer to use.

Sites using theming or micro-sites with a `SITE_NAME` not ending in `edx.org`
should not be affected.

DOCTYPE to the top of the file.

Let staticfiles determine the footer URLs

fixes template errors

keep tos untranslated

formatting fixes

the actual urls

* Fix indentation/line break issues
* Handle marketing root URL as a separate case in marketing_link
* Move link map to its own setting.

and use it for the new marketing site links.

Update links in footer to point to the right pages.
Update link on dashboard without any classes.
Update links in header.
Update links on sign in and register pages.