Demos RELAY. Create 2 *separate* clusters with RELAY as top protocol. Each RELAY has bridge_props="tcp.xml" (tcp.xml
needs to be present). Then start 2 instances in the first cluster and 2 instances in the second cluster. They should
find each other, and typing in a window should send the text to everyone, plus we should get 4 responses.
Called when a change in membership has occurred. No long running actions, sending of messages
or anything that could block should be done in this callback. If some long running action
needs to be performed, it should be done in a separate thread.
Note that on reception of the first view (a new member just joined), the channel will not yet
be in the connected state. This only happens when Channel.connect(String) returns.