Example showing controlling gui from repl

[fjames86]

Need a clear simple pedagogical example showing at least the following:

• running gui message pump from background thread ie a thread that is not the repl thread
• Sending control messages from repl (or some other thread) to gui so that it responds in some visible way
• Advanced option: sending the control message using networking protocol eg a web REST request or similar.

This would show how to write something which could be modified interactively.