Consider including a list of recommended order statuses

[mistermoe]

the orderStatus property of an OrderStatus message is effectively plaintext which becomes quite difficult to wrangle especially from a wallet's perspective. We should include a list of recommended order statuses in the spec and a description of said status.

Additionally, It would be helpful to provide these recommended order statuses as enums via our SDKs

Here's a few that come to mind immediately:

Status	Description
PAYIN_PENDING	Order has been received and PFI is waiting to receive the quoted payin amount from Alice
PAYIN_RECEIVED	the quoted payin amount has been received by the PFI
PAYOUT_INITIATED	the PFI has initiated the quoted payout

[mistermoe]

cc: @angiejones

[jiyoontbd]

• payin_pending, payout_initiated as above, and add:
  • payin_settled
  • payin_failed
  • payin_expired
  • payout_pending
  • payout_initiated
  • payout_settled
  • payout_failed
• not recommended, but strongly type the orderstatus.status with the above string value and optional details field
  • optional details field can be populated by the PFI
• need order statuses for refund flow (i.e. when we receive a cancel message) related to #341
  • refund_initiated
  • refund_pending
  • refund_failed
  • refund_settled