Display labels inside node shapes if user wants to.
Until now, labels are displayed outside of node shapes. We should allow the user to choose whether she wants labels inside or outside of nodes.
For the implementation of this feature, nodes should have bigger or even different shapes.
Implemented a not-satisfactory solution. You see labels are separate objects in our canvas, so it's quite difficult to draw them completelly inside a node. For instance, a problem is that the node should automagically 'grow' when the user inputs a rather long label...