retach/detach: folder version control or not?

Problem

1. Counter-intuitive settings in folder structure.
2. Not fully tested, so don't know what quirks it may give.

Argument

1. Why introducing folder version control? 
2. Cons: files are scattered into different folders and hard for the successive processes to load the folders.
   

Solution

1. For each FOV, if no .dat exists in attach/detach folder, first copy from filter_blob, then start from attach with overwriting.