Follow more closely what is done in the atpackager plugin

This pull request changes 2 items to follow more closely what is done in the [noder atpackager plugin](https://github.com/ariatemplates/noder-js/blob/master/build/builders/NoderPackage.js):
* instead of including the module definition function skeleton, it uses the one from `noder-js`, so that if it changes in a future noder-js release, this plugin will not have to be updated
* `findRequires` is called with `true` as the second parameter so that code using loader plugins is properly packaged (for more information about loader plugins, read the loader plugins section of the [noder-js documentation](http://noder-js.ariatemplates.com/api.html).