Dealing with pairs

VisuPair — V_Sim can draw link between nodes. This part defines a pair object and interface to draw pairs.
VisuPairSet — a base class for all loadable representation of VisuData objects.
VisuPairCylinder — An interface defining all the properties required to draw a VisuPair as a cylinder.
VisuPairWire — An interface defining all the properties required to draw a VisuPair as a wire.
VisuPairLink — An object to store rendering properties of a VisuPair for a given distance criterion.
VisuPairLinkRenderer — Defines a common class for VisuPairLink renderers.

Drawing pairs is done via external modules. For the moment, two modules exist to draw pairs : one draws flat lines between elements (colour and width are user-defined) and the other use cylinders to represents pairs (radius and colour also user-defined).