Fix version 0.2.0-dev3 and later

In this MR, version 0.2.0-dev3 (and later) is fixed:

• We use DPIAdjusting transform as it is a key component when training on images of very different sizes
• We compute the real mean and std values on the train set (we do not use default values from ImageNet = revert a5f7b5ab)
• The padding is on the right and bottom of the image (= revert part of f57bc667 for now)
• Two parameters files are created during training: one for training details (used to reproduce/continue the experiment), one for inference (that can be directly used by Arkindex DAN worker)

dan/manager/dataset.py

 # -*- coding: utf-8 -*-
+import copy
 import json
 import os
 
@@ -112,7 +113,7 @@ class OCRDataset(Dataset):
 
     def get_sample_img(self, i):
         """
-        Get image by index
+        Compute the final image size and position after feature extraction
         """
         if self.load_in_memory:
             return self.samples[i]["img"]