New option --remember-auto, to remember choices and re-apply them

Hi,

first of all, thanks for this great tool, it helped me to quickly remove many duplicate photos I had on my disk.
Now, I made this small change, which allowed me to be much faster in removing duplicates. It basically remembers my choices for a set of duplicates (ie set of directories that hold duplicate files) and then re-applies the same choice if the same set of duplicate directories ever repeats again.

This allowed me to make ~50 selections for more than 1000 duplicates. That was a huge speedup for me. Of course, your mileage may vary ;)

Cheers,