There is double maintenance right now when you change the STATIC_URL
via settings.py, you must also use a custom theme to have access to
also change $webroot within the SCSS to serve font-awesome from a
custom location.
This patch makes the STATIC_URL available by default in the SCSS
namespace through variable $static_url.
Also, it was being called $webroot in the SCSS, but it should
actually be called $static_url since it should map directly to
settings.py's STATIC_URL.
Change-Id: I1ee40652f8110b176f45b8811f0e0197789a73da
Closes-Bug: #1478794
24f25eddb6