Ping Failure Notification

[pbitzer]

Right now, we look for a ping failure to determine if the sensor can be reached, as a proxy for the sensor powered and operating as expected. When it fails, we send out a notification.

However, there can be a ping failure even when the sensor is on. (I think it is due to trying to ping while the sensor is sending out a data packet, as it primarily seems to happen during storms.)

Add a hook to wait for consecutive bad pings before sending out a notification.