Add 'ApplyAVSCV2' : '2' param to authenticate

Sagepay requires this, otherwise the following error is thrown:
5017 : The Security Code(CV2) is required.
Authenticating requires a description field

This is only required on LIVE Sagepay servers
Compatibility patch for Oscar 0.4

These were added or changed after Oscar 0.4:
- oscar.apps.payment.bankcards was added : copy it over
- address AbstractCountry's code was added : fallback to iso_3166_1_a2
- Bankcard has changed some fields : fallback to the od names