Set contact properties for caster and wheels

[IDavGal]

Webots uses the contactProperties field in the world settings to define the physical properties of the interaction between different solids with a specified contactMaterial.
This is a twofold problem:

• On one side the contactProperties sets the properties of friction between 2 contactMaterials and is configured in the WorldInfo node, which is defined in the .wbt worldfile.
• The contactMaterial is defined in the Solid node, which is being automatically generated from the andino URDF. Currently urdf2webots doesn't provide a way of setting a contactMaterial for a solid.