Fixed clone methods in core.

Since ITK introduced clone methods in their base classes MITK clone methods
collide with them. I adapted the mitkCloneMacro to be compatible with ITK.
All "Clone()" methods were renamed to "InternalClone()" and return a
pointer to a LightObject instead of an AffineGeometryFrame3D.
InternalClone() is called by ITK's Clone().