Translate's pagetranslation.uls module needs to override the action
that happens after language code is set. Currently it uses setlang
url parameter, which (no longer) works with Special:MyLanguage.
After this patch, it can use mw.uls.setLanguage and does not need
to reimplement it's functionality.
Turned mw.uls.changeLanguage into simple utility that calls
location.reload when the promise is resolved.
Change-Id: I9a648b146188dd252c239085bbe276165dc5f393
099f1f37c8