Fynbos integration

[DonChangfoot]

Fynbos has started integrating Rafiki into its backend for use with outgoing payments. Here are some thoughts and questions so far.

• Our thinking stems from the view that Fynbos and its partners hold the user's account and Rafiki is how we send instructions over the Interledger network. As such, we'd like a more explicit API when it comes to the outgoing payments. For example, the execution of the outgoing payment is implicit when you call the depositEventLiquidity mutation. Ideally, this execution step would be explicit where we provide the id of the outgoing payment we want executed. This fits more cleanly into our business logic instead of mapping an event to a payment.
• We'd also need a FailOutgoingPayment mutation - we will expose Rafiki open payments api for programmatic access. When a user creates a payment programmatically then we will receive the created webhook. We then run business logic e.g. reserve funds etc. If this fails then we need to fail the outgoing payment.
• We also need a way to see/infer whether an incoming payment is an on-us payment.
• This is a nit: the createAccount on Rafiki should be more along the lines of registering an identity. As again we provide the underlying account and Rafiki provides a discoverable identity on the Interledger network.