Bug 1061745 - Fix 404 when accessing webmaker profile (through /user) with a locale string in URL

This moves the i18n middleware earlier in the express middleware chain (specifically, before `/user` is proxied to webmaker-profile-2), so that the URL `en-US/user/erik`, for example, will be correctly proxied to webmaker profiles.

Note that webmaker-profile-2 doesn't appear to have great localization support right now, and only supports en-US.  Thus, while webmaker-profile-2 will see the correct `accept-language` header, it will promptly ignore it and always use en-US, regardless.