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
Spoiler alert: Node has a [`util.isArray(object)`](http://nodejs.org/api/util.html#util_util_isarray_object) function.