Evaluate a possibility to implement messaging with a Worker/SharedWorker

[dhuebner]

It would be interesting to try out communication with a worker thread. Following should work:

• [ ] register a worker (needs a new participant type)
• [ ] send and receive messages to a worker (from extension or webview)
• [ ] terminate worker on dispose
• [ ] maybe implement a plain HTML page new Messenger() that spawns a Worker and "talks" to him.