Prepare for publishing.

* Move `bower install` into `prepublish`.  This prevents consumers of the new published `ember-data` package from having `bower` installed globally. Also, nothing changes as far as setup requirements: running `npm install` in the root of the repo runs the `prepublish` script.
* Only publish the specific files that we want (leaves ability in the future to publish other types of things).
@rwjblue I goofed and forgot an equals sign on that `--environment=production`. Can you fix?