Bip70: payment delivered as JPP JSON instead

[monsterbitar]

When bitcoin-com's wallet gets a BIP70 payment request from my server, it properly shows it to the user and thus proves that it has parsed the protobuffer inherent in the BIP70 specification, but when payment is being sent it instead sends the payment payload as JSON according to the Json Payment Protocol.

[sonofliberty]

This, #576 and #577 are huge issues for small companies working with BIP70. I have the choice between bending my payment request endpoints to somehow deal with this mess, or warn my users that they shouldn't use the Bitcoin.com wallet to make payments on my site.