Detect when Tor is failing to connect to the network
Under some circumstances (see #845 (closed)), Tor can't connect to the network but the app doesn't realise there's no internet connectivity.. Repeatedly trying and failing to connect to guard nodes could cause Tor to mark its preferred guards as unreachable and choose new guards sooner than necessary, which could harm anonymity. We should consider setting DisableNetwork 1 after repeated guard connection failures, then waiting for a connectivity event before trying again.