Forces visualizers and extra forces

•Added a resolveinframe selector to the worldforce to be easily able to simulate forces like drag forces on a planar car.
 •Added the force and moment visualisation. Therefore some parts from Multibody had to be cloned to "visualizers" to get the pointers to the right world model.
 •Added a quadratical Speed dependant force to simulate drag forces
 •Fixed the icons from the copyright so they also work when not in the working directory