Remove commerce_bitpay_default_settings().

The array is now located directly in the settings form instead of loading a separate function.
Fix double-redirect on payment.

The redirect form was redirecting to the complete page. By changing the offsite_autoredirect to FALSE, it stays on the payment page for both the hosted payment and the iframe.
Load the correct library reference for BitPay.

IPNs wouldn't work because the BitPay php-client library wasn't loading because the IPN include file was referring to the wrong library key.