We should throttle if the server didn't response within callback cycle.

Currently continuous json callbacks happen, even if no reply ocurred. This leads to a self-initiated DOS attack in case of too many (some!) listeners.

We should wait for the callback happen and set the reload timer there.
If the server gets longer response time the loading gets throttled.

For callbacks that fail we might add another timer to invalidate previous requests and start another try. This avoids hangups that need page reload to continue.