Return close code from WebSocketClient.run/connect

[adam-fowler]

• Return close code from WebSocketHandler. This is ignored by the server but passed back to the user when using the client
• Also throw errors, caused by closing WebSocket channel, Server should report these but otherwise ignore them. Client throws them

[adam-fowler]

@Joannis this has had some minor changes

• Return close code and reason
• Added WebSocketOutboundWrite.close function to allow for users to write custom close codes, reasons