Integrated django-rosetta and created initial po file

Remaining Items:

- [x] Link Mezzanine admin to Rosetta interface
- [x] Apply grapelli UI to rosetta
- [x] Rename Simplified Chinese po directory
- [x] Docs

This puts the Rosetta menu item before any of the others-- not a blocker, but later it might be nice to have it in alphabetical order like the rest of the admin menu items.