Migration Guide: improve content on remoting URL changes

In JBEAP-2791, we clarified that server migration using only the :migrate operations will keep a lot of the EAP 6 configuration, including remoting URLs (protocol, port number).

In JBEAP-3493, we added the same info about remoting URLs to a chapter on remote JMS clients. I have a couple of comments to that:

• We are duplicating content. That isn't necessarily bad, because the chapters on server upgrade and application migration can easily have different audiences. So I'm fine with saying the same thing on multiple places.
• If we explicitly repeat the info about remoting URLs in a chapter on remote JMS clients (4.2.2. Update External JMS Clients), we should also say that in a chapter on remote EJB clients (4.9. Migrate EJB Client Code).
• The formulation in chapter 4.2.2. Update External JMS Clients is IMHO a little bit unclear. I'd prefer just saying "the remote URL changed from remote://localhost:4447 to http-remoting://127.0.0.1:8080" (BTW, why once localhost and once 127.0.0.1?) and then add a Note (or some other kind of warning) saying that "If you migrated your EAP 6 server configuration using only the :migrate management operations, then the remoting URLs didn't change at all. For more information, see the note in chapter 3.1. Management CLI Migration Operations". Repeating the part about "http-remoting://127.0.0.1:8080" once again is a bit confusing, especially if you say "with the default JBoss EAP 7 configuration" (people will their configuration, so it will no longer be default... hope you understand what I mean).