some fix: class + engine

-Only 1 choosingDate Time T
These values depend on time:
-Rate dividendYield(Time t) const;
-DiscountFactor dividendDiscount(Time t) const;
-Rate riskFreeRate(Time t) const;
-DiscountFactor riskFreeDiscount(Time t) const;

GBlackSchole and GDelta Optimisation:
Two in one function so it does not have to use BlackScholesCalculator
two times for the same option.