Make ModeManagerNode and ModeMonitorNode themselves lifecycle nodes?

- Seems natural to use the same concept (i.e. runtime lifecycle) for these to nodes themselves.
- Yet, in many applications, the mode manager node will be used continuously from system start to shutdown so that there is no need for a runtime lifecycle
- On the other hand, one might think of a distributed system with multiple mode managers for subsystems which could be deactivated during runtime.
- If making the two nodes to lifecycle nodes, convenience launch files with auto-activate functionality should be provided.