Create an HTLC payment channel for Hydra/XQuery #91
Description
An HTLC payment channel will allow clients to make significant subscription payments without fear of losing payment credit due to the SNode they paid going offline or simply ceasing to respond to data requests. With an HTLC payment channel, the client will be able to simply "close the payment channel" in such circumstances to receive a refund of the bulk of their payment.
Hopefully, much of the code from the existing Hydra/XQuery payment mechanism can be leveraged in creating HTLC payment channel support.