Implement RFC 7239 (Forwarded HTTP Extension)

[JanTvrdik]

Nette\HttpRequestFactory should support RFC 7239 (Forwarded HTTP Extension). It may be wise to wait for servers to implement it first.

[patrickkusebauch]

About to implement it in legacy Nette 0.9 Application, where we configure our own reverse proxy. Once done there, I plan to port it for Nette\Http.