Reregister push token periodically

It seems that Telegram servers disconnect our notifications if we do not reregister periodically. Set the interval for reregistering to 4 hours as TELEports is suspended in the background, and we might miss therefore the suggested 12hrs interval. Strictly speaking 6hrs would be enough(Shannon) but 4hrs wont hurt, since if people sleep during night we want to have an ASAP reregistration if they use their phone in the morning.