Tooltip default

This is a small patch, that calculated the tooltip ID from the connections.
It is enabled by setting the ID to "default". 

Not sure id this is the best way. We could also remove the drag entirely but then we need a key for no- tootips. 
We can also define that an empty ID means default.

If we finally have the original button layout we might need to change some tooltips IDs, to match with them on generated from the connection. 

What do you think about this? 

 
I still feel using the item is limiting since the tooltip ids are a different namespace than the CO items. 

What about a tooltipId property for controls so we build an explicit binding between tooltip string and control?