tweaked/idealized uproxypeerconnection interface

Tweaked the uproxypeerconnection interface so my work on socks-rtc compiles and updated samples to match.

TESTED: grunt and ran `src/coreproviders/samples/freedomchat-chromeapp/` manually, messages still flow, no console errors. 
So `config` would be passed to this argument rather than the constructor? If so, there are a number of comments regarding the constructor which should also be updated -- not to mention the Freedom JSON-like interface.

I can see how this works around the issue of interfaces for constructors, although I have to say passing the config into the constructor increases the immutability of `Pc` which I generally much prefer.