Ignore .DS_Store and other such hidden files

[roachcord3]

These types of files will cause errors as hyextract tries to get hydrus to import them. It's not as simple as saying "make sure these files aren't in your temp directory" when your OS automatically creates them. Whether you feel like making a hardcoded list of file types for various OSes that should be ignored, or you want to add an option for the user to specify it, either works for me.