Fixed css regeneration and dependency copying

I encountered Problems with sass-rails-source-maps and my Setup (rails 4.1.7, source-maps 5.0.0-beta1, sass 3.4.9), specifically:

* Dependencies weren't copied to public directory, only `application.sccs` was copied, so other scss files couldn't be viewed in Browser
* Css files weren't regenerated when changes were made to the scss files

Based on https://github.com/gaijin1973/sass-rails-source-maps/commit/9bbc89b222ad9a3a7f908d9691b568e81076d057 I did some small changes and now it works again (at least in my small test environment).