Add support for rTorrent, qBittorrent etc. watch folders

[louhisuo]

rTorrent, qBittorrent (and also many other clients) are supporting so called watch folders which works in such way that when a torrent file is dropped into a watch folder, it gets picked up by a client and torrent downloaded is automatically started (rTorrent has option for both 'start' and 'load' under 'watch' folder. In addition, at least qBittorrent supports moving a torrent file to another location after downloading is completed.

Please consider to add support via Flood UI to configure 'watch' folder location(s) and also possibility to configure location where to move a torrent file after downloading is completed.