Use CxxUtils::CachedUniquePtr for m_globalPosition in PlanarCluster and PlanarClusterOnTrack

Use CxxUtils::CachedUniquePtr for m_globalPosition in PlanarCluster and PlanarClusterOnTrack to remove mutable key word.

http://goetz.web.cern.ch/goetz/mutable_2019-07-13.html#Other_Other

nightly/master/2019-07-13T2149:Simulation/ISF/ISF_Fatras/ISF_FatrasEvent/ISF_FatrasEvent/PlanarCluster.h +84

    82	  private:
    83	    InDet::SiWidth m_width; //col, row, and width in mm
    84	    mutable const Amg::Vector3D* m_globalPosition;
    85	    const iFatras::PlanarDetElement* m_detEl;
    86	    
nightly/master/2019-07-13T2149:Simulation/ISF/ISF_Fatras/ISF_FatrasEvent/ISF_FatrasEvent/PlanarClusterOnTrack.h +119

   117	
   118	    /** The global position */
   119	    mutable const Amg::Vector3D*  m_globalPosition;
   120	    
   121	  };