Fix warnings when compiling SCSS
Fix warnings when compiling SCSS

Foundation was using `!global` for non-existing variables, which
generated a warning on our current version of Sass.

This is (mostly) fixed on the latest version of Foundation. However,
this latest version isn't included in the `foundation-rails` gem, so we
can't upgrade yet.

So we're defining these variables before Foundation does so.

See issue 12080 in the foundation/foundation-sites repository for more
information.

consul/consul,consul/consul,consul/consul,consul/consul,consul/consul