WIP: L10n string export and import

- [x] Export strings from mustache files
- [x] Export strings from js files
- [ ] Export strings from go templates
- [x] Import po files from external repo
- [x] Copy and convert po files into json
- [ ] Move FindMyDevice-l10n to mozilla-services and update reference
Not sure if you want to wrap `'parsers'` in single-quotes for consistency, or remove it from `output` and `keyword` (since I don't think either of those are reserved words, iirc). Or ignore it, because who cares.