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
Sorry, I can't comment on un-diffed lines, but should the `<title>...</title>` on line 9 above also be wrapped in `{{ "Find My Device" | l }}` magic dust?