Retrieves the value stored for a key in this properties collection, and returning
the default value if the key was not stored in this properties collection.
Looks for the application home directory by looking to the OMS_HOME variable
If not set, will use holmes within APPDATA (Windows), user.home (Mac) or HOME (Unix).
For ad-hoc relations, it creates a new RelationVO
First, for relations stored in the DataModelVO, it retrieves the specified relation by name
If not found, it searches in the ClassVO objects
This function returns the value associated with selection of the JComboList
It encapsulate the logic needed to select the right value out of the model's element (ListElmVO)
according to the type of the list (ListVo.sSaveField).