Apply interceptors for socket handshake

[wzy1935]

Should close #48.

Now interceptor can be applied to WebSocket handshake packets. Since most interceptors should not modify packets during the WebSocket establishment, they are not applied by default. They can be used by overwriting allowApplyToWebSocket() method or wrapping with WebSocketInterceptor.allow() method.

[vietj]

can you add a test to ensure the correctness ?

[wzy1935]

Tests added, thanks!