Suppression de l'utilisation d'une quantification unitaire pour faire le mode sans quantification sur le DPCM

added detiq-t modifications (save as and zoom buttons to the image window and image contextual menu + add copy image function (issues with ctrl+c shortcut)) + fixed entropy calculation + fixed DPCM predictor inversion + added information to threshold dialog about moving second threshold

The error is now stored in an Image with double values,
without restriction on these