Basic API in place

Authenticate, authorise and refund payment types work.
Ignore things in sandbox/public
Skip external tests unless --external
Store vendor tx code on audit model
Add facade to bridge between Oscar's checkout and the gateway fns
Extend sandbox to submit bankcard form to Sagepay
Add factoryboy
Add BREAD dashboard
Capture cardholder name

Sagepay require this. We extend the core Oscar bankcard form to
capture a name.
Ensure facade passes on billing address info
Test gateway calls ORM correctly

We also change the exception raised on unsuccessful responses to
PaymentError to stop showing sensitive details to the customer.
Fix billing address passing
Ensure fields are truncated before passing to SP
Treat REGISTERED response statuses as successful
Transactions can now be searched in dashboard
Adjust sandbox thank-you template
Authorise requests now work

This change also adds tests and the ability to trial this functionality
in the sandbox site.
Add simple logging
Improve pytest output

Using fancy-pants graphs in the console now.
Stop logging during tests

Which gets rid of the 'no handlers found for ...' warning that was
cluttering up my console output.