1) Modified method addSingularPluralPair.
1) Modified method addSingularPluralPair. 2) Moved method addSingularPluralPair and its test cases to DataHolder class.  3) Fixed a bug in overridding equals method in SingularPluralPair class.  4) In getHeuristicsNouns method, added code to add singular and plural pair as they are learned. 5) In addHeuristicsNouns method, added code to add singular and plural pair as they are add. 6) Method addHeuristicsNouns is revised and tested.