properly handle device_added/removed events and other additions and improvements

- all status related handling now under supporting class StatusManager -- much better organized code regarding this management
- device_added/removed events now properly managed to dynamically add and remove support for descendent platforms and instruments to keep track of associated statuses
- aggregate/rollup status updates and propagation of events refined
- also support for set_agent for the aggstatus of the platform itself, including corresponding publication of event if the new aggstatus causes update of the rollup status