Rename 'clients' to 'agents' in ControlCenter Service Library
Test service to refuse same agent to connect multiple times
Make list of Agents return list of all connected agents to all of ControlCenter Service instances
Therefore now Agents is a static property of a ControlCenterService class
Make ControlCenter Service return list of connected agents
Remove ControlCenter Service's test for returning list of connected agents when signle service instance serves all agents
Allow user to view list of agents connected to service