Tackle Fee Problem for DEX proof design

[boolafish]

Description

As an exchange, I should be able to offer a pricing model that is decoupled from the network costs of using the OMG network So that, I can incentivise to promote good market behaviours and also I can offer different market models from other exchanges.

sub story of #53

Successful Criteria

• Get a full understanding on what's the requirement for exchange fee. (Decoupled from network fee)
• Have a design/solution for fee. (Probably not like how many percent or how much, but make sure the proof or tx can take fee into consideration and have the flexibility to setup fee)

[boolafish]

Close this as this is pending business research first. Could re-open or create a new one after we have more detail.