Added download directory and sub-path support for uTorrent

I closed the previous pull request because it was very messy (https://github.com/RuudBurger/CouchPotatoServer/pull/2532), and opened a new clean one. I also moved the options to advanced settings.

The previous solution ( b7d93b8 ) didn't properly work with Windows, we had a small discussion here: mikke89@1be8d5b

I've tested this solution on both Windows and Linux, and it works as expected. This does require that the user define the download folders, either in the uTorrent GUI, or in the config file for the uTorrent server version on Linux (with the config option "download_dir").