Reset Tor polling state if guard connection is lost

If the Tor plugin loses its guard connection for reasons other than a change in the device's network connectivity (which we already detect), the plugin should reset its polling state, just as it would in response to a network connectivity change. Otherwise we could end up in the following situation:

• Hidden service descriptor published
• Stop polling
• Guard connection lost, hidden service unreachable
• Contact's hidden service descriptor published
• Contact stops polling
• Guard connection re-established
• Hidden service descriptor republished
• We never connect to the contact, they never connect to us

We already receive and log OR connection status events - the plugin should be able to use these to detect when our last OR connection closes and call the existing code for handling network connectivity changes.