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
Same comment here re: "/en-US/".
I'll also assume this comment applies to the other references below, so I won't keep saying the same thing and being a huge jerk.