Replace copy configuration with automatic copying via Webpack

As mentioned in #33, the current way how copying assets (fonts, images) work is by manually configuring paths for a copy task. This works a bit against the concept of Webpack, which should automatically resolve dependencies and then copy them.

I can provide these changes via a pull request, as I already updated this behavior in my projects which are using patternlab-edition-node-webpack. So it's tested in multiple production projects.