Improve exclusion of files and folders

Exclusion currently works best when excluding files or folders inside any folder that isn't the mods folder.

If you want to exclude, say mods/cache/mod_name, then setting !mods/cache/mod_name will, in most cases, not work, or only partially.

One way to resolve this behaviour would be to acquire the absolute paths to excluded files and folders, and then when copying files/folders, checking if the path of the file/folder about to be copied, starts with the previously acquired absolute path.