Better Sass support

This pull request essentially replaces the outdated '[sass](https://github.com/visionmedia/sass.js)' npm module with a '[sass-wrapper](https://github.com/badsyntax/sass-wrapper)' module that uses the actual Sass utility for compiling Sass files. The 'sass' npm module is an attempt to create the Sass compiler in Javascript and was written for a very old version of Sass, and should not be used as it's essentially useless. 

This change also removes the dependency on a kss.less file existing in the template. The kss stylesheet can now be either 'kss.less', 'kss.sass' or 'kss.scss' (or, this file doesn't even need to exist at all).