Convert node routing plug-in to broker plug-in

Convert the routing plug-in interface from an interface for node plug-ins
into an interface for broker plug-ins.

Adapt the existing routing plug-in that publishes endpoint creation and
deletion events for the new interface.
Rename routing_activemq_engine to activemq_routing_engine

For consistency with other plug-ins, rename routing_activemq_engine.rb
to activemq_routing_engine.rb.