Added Discrete Measurement
Fixed bug in Scale Criterion sorting
Implemented ListModel in DiscreteMeasurement
Added GUI interface for Discrete Measurement
Refactored some DiscreteMeasurementPanel and added summed probability to GUI
Fixed precision issue with total probability in Discrete Measurement
Fixed compatibility issue with Java 6
Change assert to IllegalArgumentException
Add meaningful message when probabilities don't sum up to 1.0.