Better LP fee evaluation based on virtual takers not real takers

[davidsiska-vega]

At the moment the LP rewards are distributed based on LP fees received. This is gameable. Instead calculate "virtual LP fees received in quantum" which would be the amount resulting from the of trade notional of one quantum unit, happening at current markprice, once per LP fee evaluation time step. Distribute LP rewards at epoch end relatively based on this accumulate "virtual LP fee received in quantum".