refactored project - match MVC and ext. nameverification in MeasurementD
refactored exceptions to own package
added UnitConverter and moved conversion from WeightUnit to it
mplemented UnitConverter in Measurement and added its UTest
updated UTestMeasurement to comply to changes in Measurement
commented UnitConverter
moved conversion of lengths from LengthUnit to UnitConverter
cleaned code of LengthUnit
cleaned code of UnitConverter
cleaned code of Measurement