django-oscar v1.0 compatibility around shipping

### What is the problem / feature ?

The `django-oscar` shipping method API has been altered to avoid potential thread-safety issues with the [v1.0 release](https://github.com/django-oscar/django-oscar/blob/master/docs/source/releases/v1.0.rst#shipping)
This API isn't compatible with `django-oscar` >= 1.0

### How did it get fixed / implemented ?
- Add `shipping_charge` property to the submission dict so that `apply_taxes_to_submission` continues to work with `PaymentDetailsView`
- Change the `facade.apply_taxes` signature to accept `shipping_charge`
- Change the `facade.fetch_tax_info ` signature to accept `shipping_charge` and remove the use of `charge_excl_tax` property on the `shipping_method`
- Fix tests

*Here is a cute animal picture for your troubles...*

![image](https://encrypted-tbn1.gstatic.com/images?q=tbn:ANd9GcRGNwnd6qrOy551s5jM2w5UsRKMBLj3sfaklWDgieVNC6a9PRav)