added proxy-settings to http-client

title tells the whole story.

The only thing missing is a proxied request-test.
Anybody any hints on what i could use for a test?
One possibility would be to use jetty's [ProxyServlet](http://download.eclipse.org/jetty/stable-8/apidocs/org/eclipse/jetty/servlets/ProxyServlet.html), but i have no idea how to use this.