GtMultiVolView: added multi-volume basic comparison support

Signed-off-by: Nicola Vigano <vigano@yoda.esrf.fr>

zUtil_TomoUtils/GtMultiVolView.m

@@ -135,5 +135,9 @@ classdef GtMultiVolView < GtVolView
                     'Unsupported multiple array type: %s', class(vols))
             end
         end
+
+        function handles = compareVolumes(vols, varargin)
+            handles = GtGuiMultiThresholdVolume.classCompareVolumes(vols, varargin{:});
+        end
     end
 end