Moving css preprocessing into webpack

Hi, I did an example of allowing webpack to handle the css processing instead of using gulp. I think its hot-module reloading is more efficient. 

I use stylus for preprocessing and the plugin nib for browser prefixing. 

I've checked both the production and dev builds of this approach and functionality-wise, everything remains the same. Resources are correctly generated with cache busting too. 

Because I allow webpack to handle css preprocessing, I've also renamed webpack's build folder to /static/ instead of /js/. I've renamed all references in the source files and gulp too.