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
Not 100% sure about these translation strings.
Should translators be translating everything, or just the `YouTube <span> (firefoxchannel)</span>` (and not touching the actual link itself)?