WIP: L10n string export and import

- [x] Export strings from mustache files
- [x] Export strings from js files
- [x] Export strings from go templates
- [x] Import po files from external repo
- [x] Copy and convert po files into json
- [x] Move FindMyDevice-l10n to mozilla-services and update reference
What's all this then?

I'm assuming it's a language switcher dropdown for this site, but shouldn't these langs be in some config file somewhere (like the `supportedLocales` in fxa-content-server) so we can control which options are available based on their string translation %%?