Display the additional profile fields

Oscar sets `profile` ([code](https://github.com/tangentlabs/django-oscar/blob/master/oscar/apps/customer/views.py#L206)) with the list of the additional profile fields but
templates expects `profile_fields` in the context.

I decided to stick with `profile` as somebody might already have had fixed their own template. I can change it the other way around to `profile_fields` if we don't want this micro-compatibility.