Integrate mitmproxy

[JeremyRand]

Integrate a proxy server using mitmproxy. Hopefully this will make Convergence unnecessary.

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[JeremyRand]

In #34 @indolering said the following: "Shouldn't our proxy software use the RPC interface? I doubt that, for example, Tor would use mitmproxy."

@indolering In my testing, doing a single RPC call has an overhead on the order of 2ms (note that loading a website will require multiple RPC calls -- 5 RPC calls is not out of the question). I believe (though I haven't tested) that integrating mitmproxy as an NMControl service will be much faster than that. It doesn't matter for Tor's purposes -- if they don't want to use mitmproxy, then they can just not enable that service.