Implement WebSocket idle timeout

[jfarcand]

Configuring the requestTimeout with the Netty's Provider doesn't work because the reaper's task gets cancelled once the handshake is successful. Once done, the websocket connection never times out.

[slandelle]

@jfarcand AsyncHttpClientConfig.getWebSocketTimeout was actually only used in the Grizzly provider, it was never implemented on the Netty side.
How would it behave? I get the WebSocket should get closed when idle, but should this be reported to the listener?

[jfarcand]

@slandelle should be reported with code

      1001 indicates that an endpoint is "going away", such as a server
      going down or a browser having navigated away from a page.

[slandelle]

@jfarcand thanks for the tip