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
@jrconlin This is just a stand in for something that will actually look up the string value. I tried to avoid doing the lookup here, but it's the cleanest option by a mile. Is this passable enough to merge into dev so that we can get the rest of the server side implemented?