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
Is there a reason why this is pinned to a specific SHA, or twas this just a copy-pasta from fxa-content-servrrr?