When an editor decides to submit a page for translation and only chooses
one locale, they are redirected to the new translated page's edit view.

This ensures that by default, the submit translation view redirects to
where it's supposed to go:

* When translating to one locale, go to the edit page of the new
  page/snippet
* When translating to multiple locales, go back to the parent page's
  explore view

The ability to route to an explicit "next" URL is kept if for some
reason we wanted to redirect the user to a non-default location.