Refactoring: eliminated use of VettableItem class.
Refactoring: removed un-needed method.
Workunit can now use directly parsed data instead of the DataCollection
class.
Removed DataCollection class.
WorkUnit is now provided with a ProgressManager.
WorkUnit now handles marking its previously processed items.
Moved recording processed indices into WorkUnit.
WorkUnit now handles recording when it is done.
WorkUnits now close their results writer when they are finished instead 
of waiting until the application shuts down.
Removed __getattr__ delegation from WorkloadManager.