Specify file nameing format

[PyroDevil]

Currently all files are downloaded into a image directory just as they are named + post id (i guess), there are a couple of problems with this:

1. fetching from multiple creators causes their content to be mixed together
2. not all content that is fetched are images but are still stored into a image directory
3. in some cases the date when the content was posted is more important and files should be sorted that way

A simple solution would be to allow specifying a formatting string for the file names, where variables like authorname, post-date, filename and post-id can be used to specify where the files should be stored.

[PrivateGER]

Will also be an option after the UI rewrite