Added extent() method for calculation of bounding box

GeoModelCore/GeoModelKernel/GeoModelKernel/GeoBox.h

GeoModelCore/GeoModelKernel/GeoModelKernel/GeoCons.h

...delCore/GeoModelKernel/GeoModelKernel/GeoEllipticalTube.h

GeoModelCore/GeoModelKernel/GeoModelKernel/GeoGenericTrap.h

GeoModelCore/GeoModelKernel/GeoModelKernel/GeoPara.h

GeoModelCore/GeoModelKernel/GeoModelKernel/GeoPcon.h

GeoModelCore/GeoModelKernel/GeoModelKernel/GeoPgon.h

GeoModelCore/GeoModelKernel/GeoModelKernel/GeoShape.h

...Core/GeoModelKernel/GeoModelKernel/GeoShapeIntersection.h

GeoModelCore/GeoModelKernel/GeoModelKernel/GeoShapeShift.h

...lCore/GeoModelKernel/GeoModelKernel/GeoShapeSubtraction.h

GeoModelCore/GeoModelKernel/GeoModelKernel/GeoShapeUnion.h

...Core/GeoModelKernel/GeoModelKernel/GeoSimplePolygonBrep.h

...lCore/GeoModelKernel/GeoModelKernel/GeoTessellatedSolid.h

GeoModelCore/GeoModelKernel/GeoModelKernel/GeoTorus.h

GeoModelCore/GeoModelKernel/GeoModelKernel/GeoTrap.h

GeoModelCore/GeoModelKernel/GeoModelKernel/GeoTrd.h

GeoModelCore/GeoModelKernel/GeoModelKernel/GeoTube.h

GeoModelCore/GeoModelKernel/GeoModelKernel/GeoTubs.h

GeoModelCore/GeoModelKernel/GeoModelKernel/GeoTwistedTrap.h