Local listing feature

Hi,

I code new feature I think about for some times. As you code update/deletion on server side, it makes it possible.

* Keep a list of filenames/url in a local dot file, and update it at each new upload
* Each entry in this file as an index (its place in listing file), so we can designate a file by its index instead of a link or an absolute filename.
* Add a function to list this listing file
* Add some convenience function to delete a file by its index number (avoid copy/pasting of url)
* Add some convenience function to update a file by its index. So if you keep the same local/remote association, you can just pass the index as argument and in background it retrieve the original path of the source file to be updated

Of course, if modification happen from another machine, listing may become partial or wrong, so errors can occurs.

Let me know if you find that interesting, if update may be done. You can see all my tests in my testing branch