`url_region` can be `worldwide`, this will save `restofworld` instead.

`REGION_LOOKUP` is just there for looking up regions. I didn't want to mess with `REGIONS_DICT` so that it can stay consistent with the `REGIONS_CHOICES*` values. After more thought today `REGIONS_DICT` could likely be a `dict` subclass that will treat `worldwide` as `restofworld` in `__getitem__` but that seems awfully confusing and complicated.