Share of fees at settlement to be split with PartnerFund

[jijordre]

Description

It is beneficial to a allow partners to charge extra fees on top of Hubii's fees applied to trades and payments.

The first half of the implementation was described in #54. The suggested second half of the implementation describes updated schema of order, trade and payment. It also includes the interaction with new contract called PartnerFund during the settlement of driips in Exchange contract

1. Order and payment as created in partner nahmii client will have new property of partnerTag (e.g. bytes32 type). This tag will be unique per partner. Trade will include partner tags for buy and sell orders in the respective order sub-documents. partnerTag will be included in hashes of orders and payments. Default value of partnerTag as produced by Core/SDK will be 0x0.
2. Exchange contracts will transfer Hubii's share of fee to RevenueFund contract as currently implemented. In addition partner's fee will be transferred to new PartnerFund contract (see below.)

Definition of done

• Schemas have been updated
• Exchange contract have been updated
• Unit tests have been implemented/updated

Details & Questions

This issue was created based on the following description by @markbkk:

The ability for us to add an "additional partner specified fee" over and above the based striim fee. I believe this should be expressed as an additional % over the main fee combined with volume discounts. So if partner P wants to charge double the fee as Striim itself does, then they would set a figure of 200%. If striim was charging "0.1% - volume discount" for a payment of 1,000 ETH, then partner P would add on 200% and so the overall fee would be "(1 + 200%) * (0.1% - volume discount)".

Depends on

[jijordre]

Closed by #254.