Updated arm.urdf:
- now movevable with limits close to human angels in elbow
- underarm rotates around the elbow
- upperarm is fix

Problems:
- rviz doe not show any geometry; links are represented ans cylinders in
urdf
- test it with the following line: 
	roslaunch "package name" display.launch model:=urdf/arm.urdf 
		*navigate to an existing package 
		*display.launch needed (-> see Google Drive)

To-Do:
- feed the model with data