Fixes node module ID identification

WebJarExtractor was being confused by package.json files where the root 'name' key was preceded by other nested 'name' keys (like in the 'mime' package, that I included in the tests).
Fixed by using Gson for extracting that.

Please note that this requires the mime Webjar that is not on the public repo yet, which I requested here:
https://github.com/webjars/webjars/issues/451
https://github.com/alpeb/mime