def newGroup(self, inputVolume = None, mask = None, groupName = None):
        # There is actually an issue with the following line
        # because it does not check whether the new group
        # already exists or not...
        groupIndex = self.currentGroupIndex + 1
        if not inputVolume:
            inputVolume = self.getLastBasevol()
        
        if not mask:
            mask = self.getMask()
                
        if not groupName:
            groupName = groupIndex

        self.groupedFiles.append(RegistrationGroupedFiles(inputVolume, mask))
        self.groupNames[groupIndex] = groupName
        self.currentGroupIndex = groupIndex
create a new set of grouped files
dataset/ETHPy150Open Mouse-Imaging-Centre/pydpiper/atoms_and_modules/registration_file_handling.py/RegistrationPipeFH.newGroup