Move test market data builders to trait
Minor refactorings of hedging

1. Creation of a HedgingInstrument trait that has a volume
2. Replaced SwapHedgeInfo and FuturesHedgeInfo with plain HedgeInfo
3. To avoid confusion with FuturesMarket, the terms 'riskMarket' and
   'riskPeriod' are used in hedging (and position reporting).