Added everything to our high-level API that should be needed for WebSock...

...et JSR.

* Add support for async send timeout as we need it for WebSocket JSR
* Allow to either run the FrameHandler in the io-thread or the XnioWorker
* Add support for fragmented WebSocket frames in the low-level api and make use of it in the high-level one
* Handle correctly traffic after close frame was received
* Detect if blocking operation is used but run in IO-Thread