closes knowm/XChange#3647 Added support for tinyproxy acting as reverse proxy.

[scrisini]

This will support a reverse proxy setup such as tinyproxy
when connecting to any of the supported exchanges
used
by a spring java app like this

use case
is going thr a lightweight firewall like tinyproxy

[timmolter]

dumb question: couldn't you just run nginx or something to do that?

[timmolter]

Or is it that the code in XChange for streaming somehow needs to be modified? Why exactly?

[scrisini]

HI Tim
yes specifically for streaming and the additional functionality is to bridge the gap in setting up web socket session when a proxy is used in between
Changes are

1. invoke applyStreamingSpefication on connect in class XXXStreamingExchange
2. set the proxy host and port in method applyStreamingSpec - StreamingExchange
3. Add a proxy friendly handler in nettStreamingService if proxys are given.
4. and importantly WebSocketClientHandler to manage the handshake when a proxy is used
   I hope this is considered for inclusion as there shouldn't be an impact on the main flow but will be useful for proxy based implementation
   and tinyproxy is used as a lightweight firewall to block or white listed web socket url.
   particularly important in our industry.