Path remapping for packing

This commit changes how relative paths are handled depending on weather they are nested or not.

Layout is as follows.

- ./shots/01/shot_01.blend
- ./shots/01/maps/special.png
- ./maps/generic.png

Maps to...
- ./shot_01.blend
- ./_maps/special.png
- ./maps/generic.png

modules/blendfile_path_walker.py

@@ -269,7 +269,7 @@ class FilePath:
                     return blend.find_blocks_from_code(b'LI')
 
         if temp_remap_cb is not None:
-            filepath_tmp = temp_remap_cb(filepath, level)
+            filepath_tmp = temp_remap_cb(filepath, rootdir)
         else:
             filepath_tmp = filepath