Added clone method to Geometry class
Added clone method to Geometry class

walshjon/openmc,shikhar413/openmc,johnnyliu27/openmc,wbinventor/openmc,liangjg/openmc,walshjon/openmc,smharper/openmc,liangjg/openmc,walshjon/openmc,amandalund/openmc,liangjg/openmc,paulromano/openmc,wbinventor/openmc,johnnyliu27/openmc,mit-crpg/openmc,shikhar413/openmc,mit-crpg/openmc,walshjon/openmc,johnnyliu27/openmc,smharper/openmc,smharper/openmc,mit-crpg/openmc,mit-crpg/openmc,amandalund/openmc,amandalund/openmc,johnnyliu27/openmc,shikhar413/openmc,amandalund/openmc,paulromano/openmc,paulromano/openmc,wbinventor/openmc,shikhar413/openmc,smharper/openmc,wbinventor/openmc,liangjg/openmc,paulromano/openmc