Remove helper function (CalculateEstimateType) for determining whether
estimates should be conservative or not, now that this is only called
once from GetMinimumFee and incorporate the logic directly there.
GetMinimumFee now passes the conservative argument into estimateSmartFee.
Call CalculateEstimateType(mode) before calling GetMinimumFee or estimateSmartFee to determine the value of this argument.
CCoinControl can now be used to control this mode.