Automatic save path management

[Rudo2204]

Useful for users who leech multiple packs simultaneously.
Idea: Still require save-path field to be non-empty. However, rpl will not directly set save path to this directory, but instead will create more directory inside this using the format: ${torrent_hash}_${torrent_name} (basically near impossible for it to be duplicated with other torrents, and relatively user-friendly)