Changeset 2038

• Renamed VariableImpactCalculator to VariableQualityImpactCalculator and calculate the ratio of new quality value to old quality value to get an idea how the quality value is influenced by each variable.
• Changes in Dataset to improve the speed of SetValue (only set a dirty flag instead of reallocating the caches)

#644 (Variable impact of CEDMA models should be calculated and stored in the result DB)