Set up Redis/Postgres to track async payments

[nkramer44]

In order to provide idempotent/async sendMoney functionality, we will need a data store that is able to keep track of pending/complete payments. We should decide on a data store, either Redis or Postgres. Since this will likely change with any more sophisticated balance tracking/resiliency measures, we should probably just go with what's easiest.

This should just be one table with the following fields (essentially storing a SendMoneyResult plus or minus some fields):

• paymentId : Some unique identifier which will be passed by the client. Assume UUID for now
• originalAmount : Amount requested to send
• amountDelivered : Amount that was actually delivered
• amountSent : Amount that was sent
• amountLeftToSend : Difference between originalAmount and amountDelivered
• Maybe some packet info for debugging purposes, but not necessary
• destination : Payment pointer of the receiver
• status : either PENDING, COMPLETE, or FAILED

Note that this will partially solve the resiliency issue between client and Hermes, but will NOT solve the case of Hermes disconnecting from the connector.

[sappenin]

For the future - let's do this in Postgres first.