payment request - first working version
Merge branch 'master' into payments
use jettison to generate payment request JSONs
check if the payment request is for the right network
check if payment request isn't expired
add recipient's pki name to payment request data
improved error handling of payment request loading

- openPaymentRequest* methods return NO and an NSError instead of
  calling the callback if the method throws exception on the Java side 

- more uniform error handling for local file and remote URL variants

- added codes for various errors that might happen
Merge branch 'master' into payments
improved error handling of payment request sending
include PKI authority name in json
no need to wipe aes key again after tx is broadcasted

it’s already wiped in “finally” when exiting sendCoins()
send transaction manually if payment_url isn’t set
Merge branch 'payments'