Fixed CalculationResult Bug in WhoStageAtArtStartCalculation

Fixed bug in WhoStageAtArtStartCalculation causing CalculationResult to be given a value for the WHO Stage obs even when NULL/UNKNOWN is saved in the database. See PT story: https://www.pivotaltracker.com/story/show/62142144

Added unit test for Fixed bug in WhoStageAtArtStartCalculation.

Removed hard coded concept id for STAVUDINIE and added the UUID to the Dictionary class.