Union refactoration

Changed Implementation of PEs Union-Structure to avoid redundant storage of data. Subbodies of Unions now store only their relative position to the center of the Union and there relative rotation. The global position and rotation is computed by the appropriate recursive methods getPosition() and getRotation(). This branch includes the removal of the rpos property of RigidBody and grants only private access to the properties gpos and q (Rotation), which should only be set via the Setter-Methods or constructors.