Support real remote address behind HA proxy through x-forwarded-for header

[vietj]

HttpConnection now provides a remoteAddress(boolean) that returns the local IP address when running behind HA proxy.

We can support this with an x-forwarded-for HTTP request header.

Note that any original header value should be included in the list.

[onyn]

This feature would be also helpful in SockJSSocket and WebSocketBase.