Update language pack metadata to include KA po metadata, package size

This solves #1246 and #1265.  It also restructures `update_languages.js` to remove the interdependencies between the central and distributed server requests, as well as one essentially duplicate update URL endpoint/view.

Testing:
tested with a zillion different language packs, both on central server side (creating them) and distributed server side (viewing/installing)

![image](https://f.cloud.github.com/assets/4072455/1736154/9c2a467c-6360-11e3-89e5-ea7c70cbd321.png)