Only allow warn+err lvl logging for Tor service

The Tor service logs often confuse Whoogle users, since they're a lot
more verbose than anything Whoogle ever reports. The bulk of these logs
use "notice" level logging and are not helpful for the average user, so
everything between debug and notice is now directed to /dev/null.

Fixes #825

misc/tor/torrc

@@ -6,3 +6,6 @@ CookieAuthFileGroupReadable 1
 ExtORPortCookieAuthFileGroupReadable 1
 CacheDirectoryGroupReadable 1
 CookieAuthFile /var/lib/tor/control_auth_cookie
+Log debug file /dev/null
+Log info file /dev/null
+Log notice file /dev/null