use churn rather than uproxypeerconnection

This integrates the SOCKS server with churn. Pretty simple, thanks to the identical interfaces. Depends on:
https://github.com/uProxy/uproxy-churn/pull/40

I wish there were a simple way to plug in different peerconnection providers but that seems like something to address at some future point.
"Single page" -> "Single-page"

Also, Github says the Travis build failed, presumably that's because https://github.com/uProxy/uproxy-churn/pull/40 wasn't merged yet at the time.  Before merging, if you haven't already done so, please check that the build passes.

Otherwise :+1: