All nodes use Svget and Svset

Changes in util.py and 
disabled writing to old style string propertys in each socket.
new function to support showing of socket cache data

Node_s to fully support socket data cache.
New label showing code

The following nodes are updated, please help to check them.
ViewerNode_text  
HilbertNode  
HilbertImageNode   
ImageNode  
CentersPolsNode  
DistancePPNode  
AdaptivePolsNode  
CrossSectionNode