Add Kafka support (matching what the MP portfolio now does)

[jwalcorn]

hey @BarDweller - when you get a chance, we should look at whether you can update your portfolio-spring to do the Kafka stuff for talking to IBM Event Streams, like portfolio now does (as requested for the FastStart and Think demos). presumably you'd use https://spring.io/projects/spring-kafka. would be another good comparison point of possible ease-of-use in Spring versus the approach you'd currently use in Java without it (which will get much better, once mpReactiveMessaging becomes available). we should be able to get to where trade-history can consume the message you'd post from Spring, just like it can the message I currently post to the stocktrader topic.