Function getNextAveragePrice
- getNextAveragePrice(size, sizeDelta, existingDelta, hasProfit, isLong, markPrice, existingAveragePrice): BigNumber
 Parameters
- size: BigNumber
 - sizeDelta: BigNumber
 - existingDelta: BigNumber
 - hasProfit: boolean
 - isLong: boolean
 - markPrice: BigNumber
 - existingAveragePrice: BigNumber
 
Returns BigNumber