Visual vertex representation for ReteGraph.
Base impl for all rete vertices.
Can be connected with another BaseVertex with a Connector.
author: Ahti Kitsik
Add an incoming or outgoing connection to this vertex.
Parameters: conn - a non-null connection instance throws: IllegalArgumentException - if the connection is null or has not distinct endpoints
Remove an incoming or outgoing connection from this vertex.
Parameters: conn - a non-null connection instance throws: IllegalArgumentException - if the parameter is null