-Able to redownload only missing file: when a gallery isn't properly
retrieve (missing pictures), you can now redownload only missing file. Simply start ImageSpyder
with the address of the gallery (that can be found in the directory named
after the gallery's number) that miss files, ImageSpyder will ask what you want to do either
delete and redownload, download missing files or do nothing.
-You can setup, how many times you want ImageSpyder to try to redownload
missing files after retrieving a gallery (if not successfully retrieve)