CORE-4191:
* Expanded definition of AppTemplate data model to include a DataObject
class.
* Created a util class for creating unique object (different object
references) copies of AppTemplate (and other related classes). 
* Added more null checks for arguments whose default values are not
supported. NPEs were getting generated after a new argument was dropped
and flushed through the AppTemplateWizard editor.
* Added null check for creation of new list comboboxes.