Fix runtime graph rough UI

[cdmihai]

Current problems:

• [x] initially the graph is printed upside-down ... After the first zoom or pan action, it immediately snaps to normal. May be a bug in the graph library, maybe not.
• [ ] node text is clipped. Cannot figure out how to make the node rectangle properly fit the text :(
• [ ] increase separation between graph layers, so target arrows do not get so crowded. Sadly, the only way I know for doing this, setting GraphViewer.Attr.LayerSeparation does not have any effect.