Issue 7 - ConverterUtils.jsonToMap() not able to handle 'simple' JSON Object:
* All JSON models were parsed using GrailsParameterMap, even when not required for the construction of domains
* Created a separate method for parsing simple JSON models - ConverterUtils.jsonToSimpleModel
* Renamed ConverterUtils.jsonToMap to ConverterUtils.jsonToDomainConstructionModel for purpose clarification
* Added additional test cases