Add Columnstore operations to MaxGUI

From MaxGUI, it should be possible to

• add a new node to a Columnstore cluster
• remove a node from a cluster
• stop the cluster
• start the cluster
• view the status of the cluster

The functionality for performing these is already exposed as call commands on the Columnstore monitor. However, somehow MaxGUI must be made aware that servers monitored by a particular monitor together constitute a Columnstore cluster and that they can be manipulated via that monitor.