Renamed ProgressManager to LocalProgressManager.
Added more generic methods for getting and setting properties
in VOSpace.
Changed get_property to return None if the node doesn't have the 
property.
Implemented progress manager interface using VOSpace tags.  
Testing still to be done, so this should be considered more of a sketch of 
how things will work.
WIP: setting up vospace integration tests for the vospace progress 
manager.