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
lol. It's WIP code. It'll be some magic that extracts the strings from the golang index file which is not going well :sob:.