[rtorrent] Fixed bug where setting changes would not take effect

Discovered an issue where adjustments to rtorrent downloader settings wouldn't take effect until you restart the CouchPotato server. This was discovered to cause the problems in #2801

This is a result of of how ```connect()``` on first command/request creates a persistent ```RTorrent``` object based on the current settings and is used for all future calls.

Not sure what you think of the changes in ```couchpotato/core/settings/__init__.py```, let me know if there is a better way this could be done.

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**Note:** It looks like the Deluge downloader might have this same issue as well, I suspect this will need updating in a similar way to this PR.