Use pure CSS only (for compatibility with our OBS packages)

 * In a regular setup, everything will work as expected using the asset pipeline.
 * For our packages, everything will work just copying ```application.css``` into ```[obs]/public/stylesheets/obs_factory```
 * The only drawback is that we will not have digest for ```application.css``` when deploying from our packages, but that's probably not a big deal.