Remove MessageHub references where possible and/or replace with "Event Streams"

[mrutkows]

A couple of things need to be addressed:

1. This package should be primarily a Kafka package and any IBM implementation/offering/branding should be left out.
2. If the community deems that the IBM impl. is noteworthy and benefits the project, in the current case "IBM Message Hub", we should correct the references to use "IBM Event Streams" as "Message Hub" is no longer the name and cannot be found in IBM Cloud catalog as of Sept. 2018. Please see https://www.ibm.com/blogs/bluemix/2018/09/ibm-message-hub-is-now-ibm-event-streams/

[mrutkows]

The name change was reported independently on issue #312, but the impetus should be on removal of any IBM names where possible.