New Cesium release packaging

This is a first cut at a new packaging structure originally detailed [here](https://groups.google.com/forum/#!topic/cesium-dev/ni1eAQAYbZk)

1. The original zip file has been renamed to `Cesium-amd-<version>.zip`  It includes the same content.  It's intended for people who want to develop with AMD or want a complete copy of the built tree on hand for reference. `61.5 megs`
2. A second zip file is also created, `Cesium-<version>.zip`.  This new file contains only the minified Cesium.js, Assets, Workers, Documentation, and a new skeleton app; nothing else.  It's intended for people to get up and running quickly using the traditional "single-file-per-library" approach.  It's also a much smaller file size, `6.7 megs`
3. The ant target is still called makeZipFile, it just makes two zips.
4. The new skeleton doesn't require a build process and simply creates the 3 main widgets on an empty globe (though we can change this).  The goal is that people can copy the skeleton and start writing their own app with it quickly.

Like I said, this is a first cut; let me know what you think.