Bypass the GUI when the path the single positive files are known

src/MATLAB/+Unmix/OpenSinglePosImages.m

-function imSinglePos = OpenSinglePosImages()
+function imSinglePos = OpenSinglePosImages(imagePaths)
     imSinglePos = [];
 
+    if (~exist('imagePaths','var') || isempty(imagePaths))
         uiwait(msgbox({'Choose single positive images and click cancel when done.',...
             '',...
             'A single positive image should have only one stain present in the',...
@@ -39,6 +40,12 @@ choice = questdlg(qstring,'Channel Order','Yes','No','Yes');
         if (strcmp(choice,'No'))
             return;
         end
+    else
+        singlePosFiles.path = imagePaths{1};
+        for i=2:length(imagePaths)
+            singlePosFiles(i).path = imagePaths{i};
+        end
+    end
 
     im = MicroscopeData.Reader(singlePosFiles(1).path);
     imSinglePos = cell(length(singlePosFiles),1);