Allow to clear handlers on websocket client on end

Signed-off-by: Julien Viet <julien@julienviet.com>
When setting a null handler, set the exception handler to null

Signed-off-by: Julien Viet <julien@julienviet.com>
Allow to set null handlers on HttpClientRequest and HttpClientResponse on end

Signed-off-by: Julien Viet <julien@julienviet.com>