Market mechanism for adjusting relay fees

[SCBuergel]

e.g.:

1. define epochs (e.g. 30 days)
2. during an epoch relayers can vote to increase/decrease the fee
3. the result of a voting cycle during one epoch apply to all txs in the next epoch
4. 1 message relayed = 1 vote (NB: this is gameable if sender is also relayer and thus sending a ton of msgs for free. But if there is some cost associated to that on top of the relayer fees (e.g. token burn) then this gameability is not scalable)
5. the maximal change per epoch is e.g. 50% up/down
6. the actual change is the voted change by each node, normalized by the number of msgs they relayed. Thus \sum_{all closed relayer channels} (FeeChangeValueByRelayer1 + FeeChangeValueByRelayer2) / 2 * (NumberOfMessagesSent) where NumberOfMessagesSent is the index of the payment channel tx that is used by both parties and FeeChangeValueByRelayer1 and FeeChangeValueByRelayer2 are the two parties of the payment channel that both can vote, if just one relayer voted, that value is used instead of the mean value, if none of them voted that part is skipped in the summation.