Swap phase 1

[gbalint]

Swap, Swear and Swindle is the incentivization system for Swarm. For details, see https://swarm-gateways.net/bzz:/theswarm.eth/ethersphere/orange-papers/1/sw%5E3.pdf

In a nutshell, swap is an accounting protocol to keep track of the downloads between two peers. We use the number of chunks requested and retrieved as a discrete integer
unit of accounting. In the ideal scenario of compliant use, the balance is kept around zero. When the mutual balance on a given connection is tilted in favour of one peer, that peer should be compensated in order to bring the balance back to zero.

Swap phase 1 is about keeping track of this balance

[holisticode]

Swap phase 1 is getting accounting to work.

[acud]

@holisticode isn't this already done? can we close?

[nonsense]

@holisticode maybe we should send the accounting registry to InfluxDB as well (optionally), so that we can visualise the balances. At the moment they are persisted in a file, but we don't really have any intuition about the numbers. What do you think?

[holisticode]

It is not finished yet. The last step to close this ticket (in terms of functionality) is #1026.

This PR introduces the actual balance tracking and pricing for the stream protocol.

But that PR includes the first real cryptoeconomic element of swap - the price of a message. It currently contains a arbitrary price for a message which has no base in cryptoeconomics and should be discussed. We should do this ASAP @zelig @nagydani @homotopycolimit

[holisticode]

@nonsense I agree it may be interesting to do. We would need to consider the performance and conceptual overhead of doing that. I don't think the performance overhead is huge, but I guess we should get buy-in for such a proposal.

[nonsense]

In my opinion there is no performance overhead at all - we are just checking 10 integers every 5 or 10sec.