Moved class DescriptiveStatistics into SDPreCal

DescriptiveStatistics isn't used outside of SDPreCal.
Imported relevant classes from external project "dragon"

Original author: Thomas Quante <thomas.quante@tu-dortmund.de>
Code cleanup and various improvements for imported classes
Updated license and author information for new code
Massive code re-formatting of new code
Some refactoring of rsputils, SDCalibrator, etc.
Deep refactoring on SDFitData
Changed SDMultiLineFitter to use exceptions for error handling