Cope with more error codes from Bango

[andymckay]

We are now getting back: USER_BARRED, USER_INVALID, BARRED, DECLINED from Bango, something that we never got before.

These all get caught as system errors and sent back to us. Some of them we hope Bango won't send us (support ticket filed)... but some of them sound like there's very little the use can do. Let's show a better error than BANGO_ERROR for some of these cases and stop sending a message to Sentry.