Added add,remove and get methods for targetConnectionFactories in

AbstractRoutingConnectionFactory

Added protected methods for
addTargetConnectionFactory,removeTargetConnectionFactory and
getTargetConnectionFactory so clients manipulate the map if needed

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Issue: AMQP-405
I just pushed the changes. Again, the ConcurrentHashMap breaks an existing test in RoutingConnectionFactoryTests that I did not write. I'm not sure how to fix it because it is deep down in the hashCode function. I'm going to keep looking at it but I figured you may know what it is quicker than me. Any suggestions are appreciated.