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
Mostly because it seemed like an unnecessary distinction. If we have no `dependencies` and all `devDependencies` then it seems like we should just use `dependencies` and call it a day. So that's not a great argument, but it's something. Is there a good reason to use dev instead?