make generation of monitoring trigger an optional feature

make generation of monitoring trigger an optional feature
- to be switched on by argument '-monitoring'
- introduce an interval of n seconds between monitoring triggers '-monitoring=n'
- send empty block list for not triggered events and events dropped because of the interval

This change will reduce the amount of data sent to the monitoring components, first of all
by sending only sparse triggers (configurable interval) and secondly because of the empty
monitoring filter list for all but the single triggered event per interval.