Switch to more idiomatic Sass usage

[lucperkins]

Right now, the Buffalo static assets commit what I take to be three no-nos:

• The Sass is kept in a css folder, which is somewhat misleading
• The application.scss file doesn't actually use Sass; it's essentially just CSS
• The Sass templates use tabs

These things are no huge deal, but I think that the changes I'm proposing here provide a more idiomatic usage of Sass and enhance the impression that Sass is a first-class citizen in the pipeline.

[markbates]

Thanks. Can you please open this PR against development?

Also, changing the folder from css to scss is a breaking change, the rest of the PR looks great, except for that and the wrong branch.

Can you pull the folder changes?

Thanks.

[lucperkins]

@markbates Okay, I reverted that. In a future release, I would recommend instituting that change but it's no biggie.