Monitor/prevent incorrect disabling of push notifications

[mwild1]

In some (undetermined) circumstances, push registrations, especially for the Snikket iOS app, are incorrectly missing. It's unclear why or when this occurs - e.g. is the app requesting to unregister? is the server clearing the registration? (e.g. due to errors delivering notifications)

It would be good to capture such events in the account debug information so we can track down the cause and determine a suitable fix.