Handle locale redirect

[tobypilling]

We would like to minimize the number of changes and uplifts so it would be great if the server could handle the dynamic locale being included in the URL. This may be necessary anyway, for the case of a missing translated file in the future.

So if this doesn't exist:
https://notifications-stage.thunderbird.net/2.0/eu/notifications.json

Can it just redirect to this:
https://notifications-stage.thunderbird.net/2.0/notifications.json