+ Added a JTree in EditorGui and implemented basic functionality. The
Tree is meant to give the user a better overview about what is already
in the switching symbol. 

+ (method) createnodes(DefaultMutableTreeNode topLevelName,
GeometricObject geomObj) in EditorGUI. This method keeps the JTree up to
date.

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+ I overrode the toString() method in GeometricObject to get it working
with the tree, but with further progress i will have to change this
another time.