Receiving transfers in the SDK

[christianbrb]

Description

Follow up to #1132

Finalize receiving transfers in the SDK including

• Single PR for receiving
• Include CLI optimizations
• Tests
• Knowledge sharing
  • Code Review (explanation by André)
  • Testing and reviewing the code (Thomas/Kelsos)
  • Going through the Raiden Docs / protocol together looking at the pictures (maybe enhanced by André)
• Discussion of the approach with the Raiden Python Team
• Pass CodeClimate
• Documentation
• Manual testing

Acceptance criteria

• We have got a feature flag (Disabled = default)
• In the dApp we have got an alert (Callback)
• We can use the CLI to test the receiving transfers
• The whole team understands the code
• The Raiden core team understands what we are doing

Critical Issues

• Can't recover from state loss after close/update and before settle raiden-contracts#1370

Tasks

• [ ]

[christianbrb]

Documentation:

• https://raiden-network-specification.readthedocs.io/en/latest/mediated_transfer.html#mediated-transfer-happy-path-scenario

[christianbrb]

Review by the Raiden Python Team (@hackaugusto @Dominik1999)

Notes

• Code Walkthrough by @andrevmatos
• Q & A:
  • Q: Processed still in the code A: Working with Processed and without
  • Q: Do refunds work? A: Not yet
• Remarks by @hackaugusto
  • Considering processing messages to the MS and PFS at once
    • HTTP is expensive
    • Collapsing balance proofs -> only sending the last one
  • Looking at the python code how sync issues have been solved (Race conditions MS/PFS <->client)

Supports:

• Restarts
• Capabilities
• Works without delivered
• Signature for RevealSecret

Not yet implemented:

• Refund (maybe it's going to be removed as it needs a lot of collateral)
• Monitoring Service
• The economic viability of on-chain secret registration (not needed now for protocol, we can implement later as an economic optimization)
• Reroute (not needed now, as we don't mediate yet)
• Remove Delivered (done through capabilities, can be fully removed when raiden-py does)
• Mediation (one additional epic) (out of scope of this PR, another feature, another issue)

@Dominik1999 @hackaugusto @andrevmatos Let me know, if this is documented correctly. Thanks :)

CC @GataKamsky