Added linear scaling of primitive models;
Added method for linear scaling of node size and weight in RobotFactory, e.g. required for the MMM reference model;

Added sensors to objects;
Added grasp to robot nodes;
Extended RobotIO::RobotDescription;
Allow reloading of the robot visualization if RobotDescription::KinematicStructure is chosen

add a VirtualRobot::Robot::clone function taking no parameter that just clones the robot (no renaming etc)