Use production builds of ember and ember-data for releases
Updated node-webkit to the latest version (v0.10.1)

Now that grunt-node-webkit-builder has been updated to properly support node-webkit builds >=0.10.0, we can finally bump the nw version.

The target name of all grunt tasks for building an osx version has been renamed from `mac` to `osx` (`grunt release:osx` or `grunt compile:osx`).

The `build/cache` and `build/releases` folders now have a different structure.