Translational joint

See merge request !19

it now:
* uses layouts
* can reload a robot
* can deactivate robot self collisions
* shows more information about the simulation

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

add overloads of SceneObject::getInertiaMatrix which transform the matrix into a different system (if the matrix was given at the com)

texture duplicate removal: using absolute path and filesize to determine if a texture is a duplicate

The 6DOF joint implementation was not functional and not in use.

Improve hand closing movements: close all finger elements until joint limits reached or collision detected

improve error message for "only revolute joints supported" in bullet robots (now the node name is printed)