.po file support

[leiux]

Many projects (e.g. Django) store string resources in .po files, and a lot of localization tools/services support parsing, editing, and saving .po files. I would love to introduce shuttle to solve all our localization needs, but a big chunk of our strings are stored in .po files.

[RISCfuture]

Because Square does not have any Django code, we can't put a lot of resources on this project, at least not right away.