This is a work in progress finished the 320px - 539px mobile
screen design.

LEARNER-2311

When you are on the Dashboard, or on any page in courseware, the logo
in the Header links to dashboard and the logo in the footer links
to edX home page.

LEARNER-2881

Added enterprise link, moved media kit down to second line, and adjusted styling
to avoid wrapping when possible.

2. Add site configuration overrides to theming/helpers.py
3. Move microsite.get_value from theming/helpers to site_configuration/helpers
4. Move microsite_configuration.microsite.get_value usages to site_configuration.helpers.values

if the staticfiles finder can't find the one that the footer API returns

Turns out if the string literal starts on the next line after the
translation function, then the translator comment is lost.  So, either
close up short strings, or add a dummy empty string on the first line to
concatenate with the real string.

Ugh.

SWAT-92

TNL-3137

TNL-3137

TNL-3137

* Add action text to social media links.
* Make the alt text for mobile links more descriptive.

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